Make Custom Ceramic Texture Molds For Fused Glass Art, by bgartman

This tutorial was written by bgartman and found here.   Sometimes some posts disappear as time goes by and this is such a great tutorial that I didn't want to lose it!  
 

This tutorial will explain how I make custom ceramic texture molds to create fused glass art.
Items used in this tutorial:

1) Firing the clay, and glass:
Kiln: I use a Paragon Janus 23 multi-purpose kiln (capable of firing glass or ceramics with the flip of a switch!)
kiln shelves
kiln shelf wash: Hotline Primo Primer Kiln Shelf Wash
plastic lidded container to mix and store shelf wash in
paintbrush to paint shelf wash onto shelves & molds (I use inexpensive Chinese brushes that are often used for glazing ceramics as shown in the photo)

2) Clay: MCS Porcelain P'Clay Cone 6 available at Baileypottery.com
https://www.baileypottery.com/clay/tuckers-pclay.h...

3) Glass:
Bullseye coe90 glass available at Bullseyeglass.com and other retailers
glass marbles such as Panacea Marble Accents often available at craft stores such as JoAnn Fabrics & Michael's
recycled Glass such as wine bottles, window glass, etc.

4) Items for creating texture in clay:
leaves
clay carving tools
textured objects to press into the clay including commercial stamps, found objects, buttons, etc.

5) Items for rolling out the clay:
rolling pin
rubber rib for smoothing clay
two 1/4" or 3/8" thick strips of wood
plastic backed fabric drop cloth, or regular drop cloth
cornstarch- I keep mine in a sugar shaker to make it easy to powder the surface of my clay
paper towels

Step 1: 

1. Creating the Clay Texture Mold

I've chosen a cone 6 porcelain paper clay as my ceramic medium for making texture molds because it has a very smooth surface that captures texture in great detail. The clay dries quickly, and creates lightweight molds, which is great for loading fused glass projects into the kiln and also great for storing your molds once they've been bisque fired. Most companies ship clay in 25lb blocks with a 50lb minimum. Please note that paper clays are prone to mold if not used quickly, which doesn't affect the quality of your ceramic piece, but may cause problems for people who are sensitive to mold. Most websites selling ceramic paper clay explain the pro's and con's of their products, along with firing instructions.
Decide what texture and design you're going to create. I've created wonderful texture molds from items found in my yard: lotus leaves, lily pad leaves, tree leaves. I've also hand-carved textures to create specific designs. Once you have your design in mind you're ready to start.

1. Work Surface:
Cover your work table with a drop cloth. I love using a plastic-backed fabric drop cloth because it protects my wooden work surface from the damp clay.

2. Clay:
Open your bag of clay. Use your wire tool to cut the amount of clay you need to roll out for your project. For instance, to create the large texture mold of of the lotus leaf takes a greater amount of clay than to create a small soap dish mold.

3. Rolling & smoothing the clay:
For most of my texture molds I roll the clay out to around 1/4" thick. If you're creating a deeply textured fused glass piece like a hand-carved pattern, you'll want to roll the clay to around 3/8" thick.
Follow basic clay techniques for rolling clay by using your rolling pin to work the clay slowly into a flat consistent thickness: Roll, flip the clay over, roll, flip the clay in a new direction, roll again until you have the desired thickness and size for your mold. I try to make mine molds 1/2" to 1" larger than the finished textured design in case the glass flows beyond my design in firing.
If you come across any bubbles in your clay surface while rolling the clay, poke them with a pencil tip or clay knife tip to make sure that they're gone before you proceed with smoothing and texturing the clay.
Take your rubber rib and smooth the surface of your clay, stroking across the entire surface of the clay with the rib horizontally, then vertically. Flip the clay over and do the same procedure again, smoothing the surface of the clay with the rubber rib by stroking across both horizontally and vertically until smooth. Now you should have a beautifully smooth piece of clay, ready to decorate with your textural design.

4. Texture the clay:
Sprinkle the surface of the clay lightly with cornstarch to keep your tools and leaves from sticking. Keep in mind that you do NOT want to press or cut your design completely THROUGH the the clay. Be careful to leave at least 1/8" thickness of clay in the thinnest areas or your mold may be more prone to breaking. As you create your texture, the hollows/deeper impressions in your mold will be the raised areas on your glass surface, and the raised areas on your mold will be the hollows/impressions on your glass surface.
A) If you're pressing leaves into the surface, arrange the leaves on the surface into the pattern you desire, then roll over the surface with even pressure with a rolling pin. I then like to take my fingers and press the leaves more deeply into the surface of the clay to make a deeper impression.
B) Add carved details, rubber stamps, press in objects as desired
C) It's a good idea to create a rim to contain the melted glass by slightly raising the edges of your clay from your table.

IMPORTANT MOLD DESIGN RULES:
-Make sure that your design does not include "under-cuts", or places where the surface of the clay mold juts out over carved hollowed-out areas. The glass will melt into these areas and get stuck.
-If you want to create a thicker piece of fused glass, you'll need to create a rim to contain the glass in your mold. If you do create a rim, be sure that it gently slopes OUTWARD so that the glass will release easily out of the mold.
-The smoother your mold, the smoother the glass. I like to make sure that all of the edges of my textured pattern feel smooth, and that there are no areas in my design that could create a jagged or sharp glass surface.
 
5. Dry your mold:
Follow the clay manufacturer's instructions. Paper clay is very forgiving, though all clay is prone to warping if dried to quickly. I like to leave my mold on my work table for a few hours covered loosely with a layer of paper towels. Once it is firmly leather hard I carefully move it to a kiln shelf in my garage and wait until the ceramic mold is completely bone dry. During the colder winter months I dry the molds indoors rather than in the garage.

 

Video showing how to make a plaster mold

This video isn't made for glass fusing, but it really shows how to make molds and if you use the correct glass mold making materials, you can easily create glass fusing molds this way! 

Click here to watch this mold making video.

Day of the Dead Sugar Skulls in Pâte de Verre VIDEO

 Day of the Dead Sugar Skulls in Pâte de Verre 

This is an excellent video to watch (and take notes on) for anyone who wants to make kiln glass frit casts with molds.  It lists all of the necessary materials needed to use and shows how to, in detail!   Made by Bullseye Glass Company.

Watch the video here!

Repairing a cracked or broken glass mold

#1. Magic Mender - 4 oz. container is for sale on the Slumpy's website. Use Magic Mender to repair chipped or broken slump molds. Use magic Mender to fuse two molds together. Fix hairline cracks in molds. Just apply magic mender to area to be fixed and fire at 1700 degrees F. 

Helpful Hints for Magic Mender:

While the mender is still moist, the joint will be fairly delicate, so be careful when cleaning the mold. The Menders must be fired to become permanent. Keep unused portion in jar tightly closed. The mender has a long shelf life and will not spoil! After firing, the repaired area is stronger than the rest of the mold. If you clean well before firing you’ll never know the break was there.

How to fix hairline cracks:

Use a knife tool or dermal to open the crack. (You must get the mender deep into the crack for it to work, otherwise the crack will reappear.) Dip a brush in the mender and in some water so that you have a flowing consistency. Allow the mender to flow into the cracks, then let dry. If you need a second application, do so, then clean the mold and fire.

#2. You can also use a resin based cement that is used in kiln building called "Sairset". It should be available in all ceramic suppliers.  Make the edges to be joined wet. Spread some Sairset on the joint. Wipe all of it off the working surface with a wet cloth or sponge. Back up the repair with more Sairset on the back. Wash all tools used immediately or the Sairset will never come off. When dry, fire to about 800C. , then wash the mold and you are ready to go.

Bullseye box casting tutorial

To view the original article and pictures follow this link Bullseye Glass Tips Sheet 5.

This Tip Sheet will introduce you to ways to create a reverse relief cast 
glass object with the optical clarity of a furnace casting, using plaster silica 
design elements in an open face mold assembled from vermiculite board and 
other refractory materials. In this process, there will be less waste than with 
traditional kilncasting processes and the majority of the mold will be reusable. 
The molds themselves will be of uniform thickness, allowing for even heating and 
cooling. Furthermore, the molds will not fail at casting temperature, which is 
among the most common concerns in kilncasting and one of the reasons that there 
is such a boggling array of mold recipes in use. The results are typically much 
cleaner and more predictable than kilncasting in most of the traditional methods, 
and the process is extremely easy to repeat for the purposes of making editions or 
production work.


Origins of the Method
This method of kilncasting developed as an outgrowth of an artist exchange project
in our Research & Education department with Mexican artist Rafael Cauduro. Cauduro 
had originally come to the factory to work in methods known as Painting With Light, 
but quickly became intrigued with kilncasting processes and began to make large-scale 
cast glass sculptures using traditional “monolithic” or one-piece refractory molds. 
The fabrication, handling, and technical challenges posed by making and firing 
these molds ultimately led the R&E team, assisted by Ray Ahlgren,* to begin researching 
other ways of building the molds. After the conclusion of the project, this research 
continued. TipSheet 5 will lead you through the processes that were subsequently 
developed.


Where you are going:  The finished piece
The end result will be a solid block of glass with relief imagery in the back of the 
piece that when viewed through the flat front creates a nearly holographic image. 
The top surface of the piece will be glossy and smooth. If carefully planned and 
executed, the top perimeter will have a soft, bullnosed edge. Occasionally, some 
cold work may be necessary or may be a tremendous advantage in the finished work. 
The finished block will measure about 19.5 x 19.5 x 4cm. These dimensions may be 
enlarged by adapting the general guidelines and adjusting the firing schedule.



Materials Needed
Glass: Because clarity is essential to creating a reverse-relief casting, we recommend 
using any of Bullseye’s 1800 series casting tints in billet form. Because they have 
smoother surfaces and less surface area by weight than other forms of glass, billets 
will trap less air than frit, powders, or sheet glass, and therefore create fewer bubbles
in the final piece. Billets are preferable not only for the clarity they produce 
in the finished casting, but also because they are easy to handle, cut, and load into the 
mold. The 1800 series glasses are formulated to gradually transition in color saturation 
as they go from thick to thin, making them ideal for this and other casting processes.
Other materials:
• Clay and tools for modeling design elements
• Metric scale
• Metric ruler
• Bullseye Hydrogel N (8242), or similar moldmaking material
• Mixing containers
• Bucket of water for initial clean-up
• Bucket of water for rinse
• Bullseye Vermiculite Board (8240)
• Stainless steel (deck) screws
• Bullseye Investment (Plaster-Silica) (8244), or similar refractory investment material 
• Fiber paper (7036)
• Vaseline/petroleum jelly
• Murphy Oil Soap
• 946 ml Ziploc food storage box, or equivalent
• Garbage can with liner
• Self-lubricating glass cutter
• Hammer




Notes on Metric measurements
For the sake of simplicity, all units of measure in this TipSheet are Metric. 
The decimal format of the metric system and its direct and simple translation from 
length to volume to weight in water makes it a superior system for laboratory work.
in the metric system: 1 cubic centimeter (cm3) of water = 1 milliliter (ml) of water = 
1 gram (g) of water.  If the interior of an empty box measures 20 x 20 x 2.5 cm, 
then this interior has a volume of 1000 cm3. 1000 cm3 of water is equal to 
1000 ml of water, which is equal to 1000 g of water. Bullseye glass is 2.5 times denser 
than water, so it would take 2,500 grams of Bullseye glass to fill this same volume.

Making a mold for multiple copies of a model
preparing a model using clay or a found object:
Prepare a model no larger than 5 x 5 x 3 cm using either water- or oil-based clay. 
This model will be used to make the design elements that will create the reverse 
relief imagery in the final casting. Water-based clay is usually softer than oil-based
clay, can be modeled very quickly, and can be reused and recycled. However, it 
will dry out over time and will shrink as it does so. Oilbased clay is usually firmer,
does not dry out, holds fine detail very well, is reusable, and releases very easily 
from most mold materials such as alginate, rubber, and silicone. Found objects 
may need to be coated with a release, such as Vaseline or Murphy Oil Soap.



For this particular process, the model itself should have minimal undercuts. 
Undercuts on found objects can be filled in with clay. The very bottom portion of 
these design elements will end up being submerged in investment material to 
hold them in place in the final casting process, so plan accordingly.




Preparing to pour a mold:
Place the model into a box with a minimum of 15 mm
of space all around it; a 10.5 x 10.5 x 9 cm flexible plastic food storage box (Ziploc)
with a slight draft to the sides works well. The box serves as a coddle system, or 
a set of dams, into which you will pour the alginate to make the mold. Use something 
like petroleum jelly to secure the model to the bottom of the box to keep it from 
moving or floating once you have poured in the mold material.


Types of flexible mold material 
for casting multiple copies:
Hydrogel N mold compound is a type of alginate that is fairly easy to mix and sets in 
5-10 minutes. It is somewhat weak with a short working life and will dry out 
and shrink over a couple of days, but if kept in a sealed container and treated carefully, 
it will usually last a few weeks.

RTV Rubber (Room Temperature Vulcanizing) is activated at room temperature but can have long set times and often takes 24 hours to cure into a very durable, very strong material.
For the sake of expediency, we have used Hydrogel N to illustrate this TipSheet.

Mixing hydrogel N mold compound:
Measure box/coddle system—including 1.5 cm above the model in the calculation. 
For our specific box and model, this is 10.5 x 10.5 x 4.5 cm, which equals 496 
cubic cm, which means that it will take 496 grams of water to fill the box to the 
appropriate level. The manufacturer of Hydrogel N mold compound recommends 

mixing it 3 parts water to 1 part Hydrogel N by weight and adding the mold 
compound to the water, but we have had good success mixing it 4 parts water to 1 
part Hydrogel N by weight and adding the water to the Hydrogel. For our project, 
then, we will need 496 grams of water and 124 grams of Hydrogel. We have 
had the best success mixing this with a spatula in a bowl using a folding, not a beating 
motion, to avoid creating bubbles in the mix. Work in a well-ventilated area and 
wear a NIOSH-approved respirator whenever working with powdered materials 
or dusts.


Pouring the hydrogel:
Be certain that you are working on a flat and level surface. Pour to one side of the object
in a flowing motion to keep air from getting trapped on the surface of the model. 
Vibrate the worktable so that the air bubbles don’t get stuck to the model.


Cleanup:
Using water immediately makes a mess. Allow remaining Hydrogel to dry in the
container and then immerse in bucket of water for initial clean up. Once cured, it is 
possible to peel the Hydrogel out as a skin. Never pour into a sink.

Removing the mold from the coddle box:
Turn the coddle box upside down on the work table and squeeze and push the flexible 
walls to let air into the sides until the mold drops out. Turn the mold over 
again and squeeze it and push carefully to force the clay model out. You now have a 
flexible mold for pouring multiple copies of your model in another material.



Making design elements out of refractory mold material
Many different refractory mold (or “investment”) materials and recipes exist. In our 
factory Research & Education department, we use a simple mixture of 50% #1 Casting 
Plaster and 50% silica flour (295 mesh) mixed by weight.


Measuring mold material:
Measure the original model and overestimate its size; it is better to discard some 
inexpensive investment than to run out and have to quickly mix more. Our model is 
roughly 5 x 5 x 5 cm = 125 cubic cm. Referring to the Investment Ratio chart on page 8, 
we can add together the amounts of material needed for voids of 100, 20, and 5 
cubic centimeters to get the proper quantities of water and investment required for 
our 125 cubic centimeter void. This means that we will need 79.99 grams of water 
and 139.98 grams of investment. Weigh these materials in clean, dry buckets. Remember 
to work in a well-ventilated area and wear a NIOSH-approved respirator whenever 
working with powdered materials.


Mixing investment material:
Steadily sift all of the required investment into the water. An island of dry material 
will begin to form once you have sifted most of the material into the water. Allow 
the investment to fully hydrate/become saturated. If left alone, the investment can 
sit for quite some time. Once the mixture is saturated, dip your hand in and 
break up any chunks. Feel the consistency. You want a creamy texture. Mix the 
investment by hand for 3–5 minutes or with an electric mixer/drill for 1–2 minutes. 
This will cause the plaster to begin to work so that it will subsequently set.


Pouring the mixed investment into the mold:
Be certain that you are working on a flat and level surface. If you have a lot of fine detail,
begin by brushing some investment mix into the details in the mold, which will 
break the surface tension so the mix can go into the details. Aim for one place in 
the mold and pour in a flowing motion to avoid creating bubbles. Once 
you have finished pouring, vibrate the work surface to make certain that no air is 
trapped within the details of the mold.

Cleanup:
Clean investment mixing buckets right away. Old plaster in mixing buckets, on hands
and/or on tools will cause subsequent batches of investment to set before 
you have a chance to pour them. It is good to use black
or colored buckets so that you can easily spot old plaster in them. Never pour
investment into a normal sink as this will clog your pipes. Pour excess investment into 

a garbage can that has a liner in it. From there, have two buckets of water to use in your 
cleaning operation: one bucket for cleaning and scrubbing the mixing buckets and one 
bucket for rinsing them. When these buckets become too filled with waste investment to 
continue using them, allow them to settle, then pour off the excess water and dispose 
of the waste investment in garbage bags.

After investment has set up:
It usually takes 5-20 minutes for the investment to set. Lightly touch the surface of the 
investment to test its hardness. Once it has set, the plaster/silica design element can be 
removed in the same fashion that the clay model was. Immediately after setting, the 
design element will still be a little soft, which means that it can be easily modified 
with simple clay tools at this point. After the design element hardens, it can still be 
modified, but you may need to use power tools for the sake of speed.  Store the 
alginate/Hydrogel mold in a closed container for later use, being careful to keep 
it from drying out.





Building the box mold with vermiculite board

Vermiculite board:
Vermiculite has a bad reputation because it is often mined in the same places as 
asbestos, which can contaminate the vermiculite. Bullseye Vermiculite Board comes 
from a mine that is certified asbestos free. It is stronger, more durable, and less 
expensive than most fiberboard and can be cut and tooled like wood or particle board. 
Work in a well-ventilated area and wear a NIOSH-approved respirator whenever 
generating dusts.  If you want your finished piece to be level and square, it is 
important to cut the vermiculite boards accurately. Also, pre-drill and countersink 
screw holes so the board does not bloat or blow out when you screw it together. Use 
stainless steel screws to put the mold together as they will hold up to repeated firings 
without flaking. Do not use galvanized steel screws because upon firing, the galvanization 
will release toxic fumes and the screws will flake and cause contamination in your kiln.
Cut two long side boards at 25.5 x 9 x 2.5 cm, two short side boards at 20 x 9 x 2.5 cm, 
and one base board at 25.5 x 25.5 x 2.5 cm. Lay the boards out as an open box 
and pre-drill holes in the flat surface of the long side boards to connect them to the ends 
of the short side boards using a bit that has a diameter slightly smaller than the diameter 
of the stainless steel screws. Be sure to drill your holes on center to avoid blowing out the 
side of the board. Then screw the sidewalls together. Next, set the base board on top of the 
assembled side boards and pre-drill holes to join it to the sides, and then screw it together. 
Then take the entire box apart and fire the vermiculite board at a rate of 500°F (278°C) 
per hour to a temperature of 1580°F (860°C) or about 55°F (30°C) higher than the temperature 
at which you will cast the glass. Hold at that temperature for half an 
hour, and then crash cool the kiln.Once the boards are cool, take them out and 
reassemble the sides using the stainless steel screws. Cut a piece of 3 mm fiber paper at 
25.5 x 25.5 cm and set it on the base board, then set the assembled sides on top of the fiber 
paper, and screw the box together. Line the side walls with 3 mm fiber paper, making sure 
that it fits tightly, without bowing or leaving gaps in the corners.

Affixing design elements within the box
The design elements must be held firmly in place for the glass casting process. To hold 
them, a shallow layer (or “bed”) of investment is poured into the bottom of 
the box around the design elements.  Hydrate the plaster/silica design elements by soaking 
them in water until the bubbles quit rising (5-10 minutes). This helps to keep the
plaster/silica bed from sucking in around the design elements due to differences in 
humidity. Arrange design elements on the interior base of the box. Check once again to make 
certain that your work surface is flat and level.

example
Measure the inside of the box to determine the appropriate amount of investment
material needed. Our box is 19.5 x 19.5 cm, and we need enough investment to 
fill it about 0.5 cm deep. Thus, the investment needs to fill a void that is 190 cubic 
centimeters. Referring to our investment (plaster/silica) mixing table you will see 
that there is a batch listed for 200 cubic cm, which will be more than enough.
Mix the investment according to the previous directions and pour it quickly and
evenly. Avoid pouring the mix directly onto the design elements or the side walls. 
Vibrate the work surface to make the investment level out.Set aside the box mold 
for 24 hours to make sure that all of the plaster/silica components of the mold have 
cured to an adequate hardness. As with the design elements, you may choose to
modify the affixing layer of investment.


Selecting glass
You may select any form of Bullseye glass to fill the mold (billet, cullet, sheet, frit, etc.), 
but the form that you select will have a direct impact on the clarity of the 
casting. The smaller the form of the glass, the more air bubbles in the finished piece, 
the less optical clarity. Powders and fine frits will create so many air bubbles 
that even our Crystal Clear 1401 will appear milky white and opalescent when used 
at this 4 cm thickness.Because this is a reverse-relief casting and the intention is to see 
the imagery created by the design elements through the surface of the finished piece, using 
billets will give you the desired clarity.

Calculating glass to fill the mold:
Measure the inside of the box mold. Then figure out the cubic volume. Use a specific 
gravity of 2.5 for Bullseye glass to calculate how much glass will be needed to 
fill the mold to the desired thickness. (Bullseye glass is approximately 2.5 times 
heavier than water.) 


Our box mold:
19.5 x 19.5 x 4 cm (desired thickness of casting) = 1521 cm3
1521 x 2.5 = 3802.5 (grams of glass needed)
This does not account for the displacement of glass caused by the design elements.
If you would like to account for the displacement caused by the design elements or if you 
have an irregularly shaped mold, you can use rice for a more precise measurement. 
Fill your mold with rice to the desired thickness of the casting. Then remove the rice 
and decant it into a container. Level the rice, and then mark the level. Remove the rice 
from the container, and weigh the container. Then fill the container with water 
up to the former level of the rice, and weigh it again. Subtract the weight of the container 
to get the weight of the water. It will take 2.5 grams of Bullseye for every 
gram of water.Use a reliable scale to weigh out the amount of glass you will need.

Cutting the billet:
Use a self-lubricating glass cutter to score glass and about the same amount of pressure 
required to score 3 mm sheet glass. It is always easiest to break the score if it is made 
along the centerline of the piece of glass. In other words, cut the billet in half, then in 
half again, to get the appropriate sizes to fill the mold.


Find the score line and break with big running pliers. Or hold the billet in a gloved hand 
and use a hammer to open the score by tapping on the back of the glass underneath the score 
line. (This does not take a lot of force; a tap exactly under the score line will cause the 
score to open cleanly.) Hold the billet low and over the table so it does not fall on your 
foot. Remember to wear eye protection.

Loading the glass into the mold:
Clean and dry the glass thoroughly, making sure to remove stickers. Any glass that is 
going to be lower than the thickness of final piece can be against the mold wall, but 
be careful not to indent the fiber paper because it will create a bump on 
the finished glass piece. Stack the rest of the glass into the center of the mold.


Loading the mold into the kiln:
Make sure the kiln is level and make sure the mold is level. Set the box mold on kiln 
furniture/posts, establishing three points of contact at least 2.5 cm from the floor of the 
kiln. This will allow heat to circulate all around the mold. If you would like to
intentionally create a wedge shape, you may set up the mold on an angle; but make 
certain that you have enough glass to cover the design elements, and that you adjust your 

annealing schedule to accommodate for the thicker area in the casting. If, for example, 
you would like a wedge that is 5 cm on the bottom and 2.5 cm on top, you will want to 
support the end that will be thicker on 2.5 cm kiln furniture, and the end that will be thinner 
on 5 cm kiln furniture, and then calculate the glass as if you were casting a rectilinear 
volume with a thickness of 3.75 cm.

Firing the piece
Vent the kiln at least up to 1100°F (593°C) to make certain that all of the moisture has
escaped the kiln. Plan to be present when the kiln is at casting temperature, and visually 
inspect the piece to make sure the casting is going as planned. If unwanted bubbles 
are present on the surface or just below the surface of the piece, plan to extend the hold 
at casting temperature until the bubbles have burst and healed.  Firing schedules provided
are specific to the Paragon GL24AD kilns that we use in our factory Research & 
Education department. All kilns fire differently. You may need to adjust the firing 
schedule for your specific kiln and project.  After the entire firing cycle is complete, we 
recommend leaving the piece in the kiln at room temperature for at least a day before taking 
it out to divest it.


Cleaning the finished piece
Remove the piece from the kiln and disassemble the box mold. Remember to wear an 
approved mask while handling the fired fiber paper and investment materials. Watch 
out for any sharp points if the glass has clung to the side walls of the mold.
The investment can be removed from the glass with a variety of tools, such as dental 
instruments, wooden picks, nylon brushes, and wood carving tools. Wooden 
tools are ideal for carefully removing broad areas of investment, and metal tools should 
be used delicately to clean fine details. A nylon bristle brush and forced air are also 
great tools for cleaning areas of residual investment. Most of the investment should be removed 
from the glass before submerging it in or scrubbing it with water. While water can be 
used to rinse away residual investment, we have found that scrubbing the glass with 
vinegar and/or CLR* breaks down the investment material.  Remember that you can create
a very different effect if you decide to coldwork and/or polish your piece. The optical 
qualities can change substantially, especially with coldworking on the edges.

How to use glass casting molds, tutorial

This tutorial came from GlassCampus.com and is full of excellent information.   Check out their website for many more informative tutorials!


Using Casting Molds

PREPARING THE MOLD
Carefully clean the mold to remove any dust and
scrub out any remaining kiln wash from previous
firings.  Single-use kilnwash like “Hotline” is
preferable to multiple-use kilnwash like “Bullseye”
because it’s easier to scrub out.  An old used
toothbrush is an effective tool for removing kilnwash
or a bristle brush on a Dremel will speed up the job.
Prepare the mold with 3 or more coats of thin kiln
wash.  More thin applications are better then few
thick coatings.  Be careful to not apply so much kiln
wash that you fill in all the detail in the mold.  Don’t
just coat the inside part of the mold that will be filled
with glass, but also coat the top upper surface.  Any
small pieces of glass that are left on that surface
will become permanently embedded into the mold if
you don’t.

FILLING THE MOLD
The glass level will drop as it melts into the mold.
Take care to be sure you  have enough to fully fill
the mold.  The smaller the pieces of glass you use,
the less it will sink.  On average, the finished
casting will be about half the depth of the loose
filled mold.  Because the glass level drops, you may
prefer to fill part of the mold with a pieces of glass
stood vertically to provide the extra glass needed to
fully fill your mold.

FRIT & POWDER
Glass powder and very fine frit doesn’t stay
transparent but will turn slightly opaque making the
finished casting looking more like alabaster then
glass.  Some attractive special effects can be
achieved by putting small amount of glass powder
in the details of the casting and filling with larger
pieces of a different colour.

FIRING SCHEDULE FOR CASTING (COE 96)
1. 800 dph to 1475°F hold 20 min
2. FAP to 960°F hold 30 min
3. 600 dph to 300°F OFF

FINISHING THE CASTING
Your casting will have some spikes along the
edges.  You can cold finish to remove them – either
by hand or with a grinder or wet belt sander.  The
casting will also have some texture from the mold.
You can remove the texture and smooth off the
scratches from cold finishing by turning the casting
over and returning it to the kiln to fire polish.

FIRING SCHEDULE for FIRE POLISH
      1    500 dph to 1000°F hold 20 min
     2  1500 dph to 1300°F hold 5 min
     3    FAP to 960°F hold 60 min
     4    500 dph to 200°F OFF min

The above firing schedules are for COE 96 glass.
For COE 90 add 20°F to all top temperatures.
For float glass add 50°F.

Chunk glass casting video

This video was made by the Corning Museum of Glass and shows how a chunk glass casting is done!

Click here to view the video!

Types of glass and their applications

Sheet glass

Sheet glass is used for the construction of stained glass windows, mosaics and fused glass art. When cut into thin strips it can be used for lampworking and when crushed it can be used as frit.

Glass rods

Glass rods are used for lampworking and kiln fusing (if used with compatable glass).

Frit

Frit is crushed glass; fine, med, or coarse sizes.  It can be used in lampworking and fusing to add color to other glass used in an art glass piece.  By filling a glass mold with frit,  you can make cast glass art.  Fine frit can be used for freeze and fuse applications as well as glass clay.

Stringer

Stringers are thin and round spaghetti-like looking pieces of glass used in hot glass applications such as lampworking and firing in a kiln.

Noodles

Noodles are a lot like stringers except that they are flat and a little larger than stringers.  They can be used in the same applications as stringers.

Casting billet chunks

Casting billet chunks are used for casting glass in a mold and other kiln applications.

Jewels

Jewels can be faceted or cast glass.  They are used in stained glass windows.

Nuggets

Nuggets, or glass globs can be used in stained glass windows (when foiled), fusing and mosaics.

Rondels

Rondels can be used in the construction of stained glass windows.

Glass Powder

Glass Powder can be used in lampworking, fusing, glass painting (that would be fired in a kiln) and glass clay.

Dalles

Dalles are slabs of glass that are used in Dalle de verre art.

Excellent glass casting tutorial from http://www.system96.com/Pages/CastingTutorial/billets.html

I didn't create or have anything to do with this tutorial below but I have discovered that when I really like something on the internet, I have to make some sort of copy of the information just in case it disappears later on and I can't find the information anymore.  This is a System 96 casting tutorial.   It is full of detail and very valuable information.  Hopefully you find this tutorial as wonderful and helpful as I do!

KILN CASTING A GLASS TABLE WITH FUSIBLE BILLETS

The August 2001 issue of Glass Craftsman magazine, presented an overview of how to create kiln-cast architectural slabs and sculpture using casting billets. Here are more detailed steps and explanations about the open face mold process. These steps describe creating a thick, cast glass slab 15"x15"x .75". This technique can be scaled up to much larger sizes with only minor adjustments in the annealing schedule.

Overview of this project

A clay positive is formed. A mold box is built around it. Mold mix is poured onto the clay positive and allowed to set up. The mold box is removed and the clay is removed from the plaster. The new plaster mold is dried and then filled with glass and glass elements. The elements can be frit, stringer, noodles, cane, billets, billet chunks or sheets. The plaster mold, filled with glass, is kiln fired then annealed. The plaster cast is broken away to remove the cast glass object from the mold.

Step #1 Form a clay positive

slab is size and shape of finished piece

A 3/4" thick slab of clay is rolled out for the positive model.

Place clay on a sheet of heavy paper on top of a smooth flat surface, such as a Formica topped counter.

slab is size and shape of finished piece

Step #2 Detailing clay positive

A variety of relief details are possible including undercuts and extremely fine details. Finer clays will give more detail while coarser, rougher clays yield less detail. This "waste mold" process requires no mold release coating.

no mold release coating is needed

undercuts are fine

Step #3 Build mold box

Trim away excess paper around the perimeter of the clay positive. Set up a mold box around the clay using 3/4" thick boards, on all four sides. Leave about 1" clearance between the edge of the clay and the mold box. The height of the mold box should be 1" above the highest point on the clay positive.

mold boards used around clay positive

Step #4 Apply splash coat

Face the clay positive with a thin creamy layer of plaster called a "Splash Coat". Pour a steady thin stream, approximately 1/16" to 1/8" thick, trying to flood it on evenly and not trap air. This coat provides a nice release surface and is soft so it pulls away easily from the glass keeping the fine details of the cast.

Splash Coat recipe (by weight):

1 part Pottery Plaster #1 1 part 200 mesh Silica add water to make a creamy consistency

"Splash Coat" acts as mold release

"Splash Coat" is soft and will keep the fine details of the cast

Step #5 Fill mold box with plaster

Use "Gerry's Mold Mix" to finish filling the mold volume. It is a stronger, coarser material than the Splash Coat. The casting mix should have the consistency of a heavy cream. It should flow into the mold box, not so runny that it flows under the box not so thick that it traps air.

over fill mold box slightly

When the plaster is starting to set, it is screed off the surface with a straight edge leaving a flat surface. This insures the top surface is parallel to the bottom. It is this flat surface that will be flipped over and placed onto the kiln shelf.

excess plaster screed off

plaster mold setting up undisturbed

Step #6 Remove clay

After the plaster has set, the mold box is removed.

carefully remove clay

Allow plaster to set at least 30 minutes before flipping over and removing clay. Save clay for weighing when calculating glass weight later. Wash mold gently to remove any clay residue, any small repairs or changes to the mold face can be done at this time.

Step #7 Dry empty plaster mold

Dry mold with or without forced air or heat for several days. This releases a large amount of water. After air-drying finish drying the mold upside down in your kiln. I ramp1 minute to 200F, hold at 200F for six hours, ramp to 600F over 12 hours then turn off the kiln and let it cool. The plaster mold should be as dry as possible. When the mold is really dry, it will be more stable, be less apt to warp during the glass cast firing and leave a cleaner glass surface. However because the molds are so dry, they have to be handled with care. Try not to handle them too much. If possible just turn them over and fill. 

dry plaster mold ready to fill with glass

Step #8 Filling plaster mold with glass

Billets

Hand cast billets, 6" x 9" x .75" glass "bricks", are a great way to get very clear castings in a range of colors. This form lends itself to casting large-scale tiles/ slabs/ panels very quickly. The colors are consistent across multiple molds and multiple firings.

System 96 Casting Billets

How to fill your mold with glass

Filling molds requires some calculating. It is necessary to determine the volume of glass needed to fill the mold volume. Weigh the clay removed from the mold then add 20%. This weight should be the corresponding glass weight needed. For simple square or regular shapes fill volume at the rate of 2.5 grams per cubic centimeter or 156 lb per cubic feet.

Once the amount of glass is known, place the glass in the mold covering the entire mold surface. If using billets or sheets to fill your mold, leave a slight gap between the glass and the mold walls. This will prevent touch points (that can be very sharp) from forming. Pile the remaining glass in a shallow mound highest in the center and also over deep cavities. If using sheet glass or billets, make sure the glass is clean! Dust and contaminates like fingerprints can show up in the cast and can contribute to devitrification. As the glass starts to melt it will flow down into the mold details and then flow out to the mold wall and level out. Mounding the glass in the center provides enough material to move toward the mold walls first and then to roll up the side, forming a nice smooth edge.

various frit sizes and colors added to mold cavities

added cane elements to mold

casting billets used to fill up the mold

Step #9 Firing Schedule

Firing glass and firing clay are different. Clay requires most if not all the artist's time and attention focused on the climb in temperature and the time spent at the top of the firing temperature range. Glass on the other hand is less concerned with what's happening as the temperature goes up, but is very concerned with the rate at which it is cooled. Slow and careful are the watchwords for successful casting. Below is a firing schedule for this project using billets. A digital controller is the best way to follow this schedule.

Uroboros offers firing schedules, in table format, downloadable from the "specifications" section of their website. Their schedules cover the use of sheet glass in addition to frit and billets when casting.

Stage A	Ramp from room temperature to 1000° in 4 hours. Mold is dry. This is probably too quick for large sheet pieces but works fine with billets.
Stage B	Hold and Soak at 1000° 1 hour Time spent here pays off later in the firing. Let the kiln and contents soak to even out the temperature. Keep in mind that a pyrometer is reading the air temperature in the free air of the kiln; the temperature in the center of the mold can lag behind that reading. The dry mold is acting as an insulation layer so it takes time for the heat to penetrate into the deepest areas of the mold.
Stage C	Ramp to 1000° to 1550° in 4 hours Slow enough so the billets slowly melt together and squeeze the air out as they also slowly flow into the relief and out to the mold walls.
Stage D	Cool to 1525° over 1 hour Bubble management. The glass is slowly getting stiffer so any bubbles are being held under the surface. Here the glass is being given the time to melt and level out. All kilns are different and these temperatures may need some adjustment. For example, 1550° in one kiln may read 1575° in another.
Stage E	Cool to 1000° as fast as possible, venting kiln if possible Quick cooling here minimizes surface devitrification (surface scum).
Stage F	Soak at 1000° 1 hour, stabilize temperature prior to annealing Again, let kiln and contents reach a temperature equilibrium.
Stage G	Anneal to 800° over 12 hours
Stage H	Cool to 500° over 6 hours, then turn off This cooling cycle is for my, slow cooling, fiber walled kilns. If you use a quick cooling brick kiln, add Stage I.
Stage I	Cool to 100° over 2 or more hours. Remember, the mold is quite a good insulator, so the glass is only cooling through the top face.

The work can safely be unloaded when the kiln is off and the glass is barely warm to the touch. Again, if the glass is large or thick or complex, waiting longer to unload is better than unloading too soon. Slow down. You risk breakage if the interior of your piece is significantly warmer to the touch than the surface, when glass is unloaded and the mold is broken away. If there is too much difference in the air temperature and the glass temperature, the glass will break. With large or thick work the kiln can be opened and several layers of newspaper laid down on the glass. This will give a tiny bit of insulation to the face while giving the glass still in the mold time to catch up, but it is not as safe as leaving the kiln closed longer.

fired glass mold coming out of the kiln close-up of fired glass in mold coming out of the kiln Step #10 Breaking the mold away from the glass This is the fun part. You finally get to see the glass! The molds made with "Gerry's Mold Mix" can be broken away by hand quite easily. Care should be taken with fine or fragile details. Running water and a stiff brush will scrub off remaining mold bits. Also a pressure washer works well to remove any mold bits, especially from rough surfaces or deep cavities. mold material carefully broken away from the glass casting detail of fired casting Here is the finished cast table!