Detailed glass casting information

We found this detailed information on creating molds for glass casting on http://www.digitry.com/glasskitchen/5castcorn.html by Susan J. Longini and Mary Bayard White.  It has a lot of great information for any glass artist interested in learning glass casting!  

Finished corn, billet and frit

CAST CORN à la Cire Perdue

The Bay Area natural foods tradition prompted us to prepare corn on the cob glass multiples by casting rather than genetic modification. The cire perdue (lost wax) process involves making a negative mold of the corn, pouring a wax positive into it, investing the wax, melting the wax out and melting glass into the investment. The molds that offer the best detail for pouring over 4 waxes are often rubber molds with a plaster backing. They are time consuming and expensive to make, but worth it if one wants to make many multiple waxes. Silicon and dental alginate molds hold up for about four pours and provide a less costly and faster alternative, as in this situation. Two recipes for making the wax corn, and two mold recipes for casting the glass corn follow. Special thanks to Mitchell Gaudet for his casting/cooking wisdom.


Cire Perdue Corn Positive à la Silicon Mold

This recipe is inexpensive, durable, quick, and can produce approximately four decent waxes. The mold is temporary.

Ingredients and Equipment
One cob of corn with a hole drilled through stem and threaded with string
Razor blade and 20 hat pins
5 cups bees wax or Brown Victory wax, enough for four corns
Pot to melt wax in: double boiler, crock pot, preferably with temperature controller
pouring cup for wax
2 tubes GE Silicon Rubber I (not II) and tube dispenser
2 tablespoons Dawn liquid soap
4 cups water

 

Steps
1. Attach cob of corn so it can hang securely from hook or beam. Hang mold without touching anything.
2. Dissolve 2 TB Dawn liquid soap into bowl of water and squirt out entire tube of Silicon Rubber into bowl of water.
3. Thoroughly mix with hands, immediately pat onto the corn until evenly covered to 1/2" in depth. Mix up a second tube of silicon immediately and apply if silicon layer is not at least 1/2" thick. Use second tube of silicon if necessary to cover the corn to the right thickness.
4. Cure 24 hours. Some silicons need longer.
5. Use razor blade to cut down the side of the wax corn through silicon about 4" so the corn cob can be carefully pulled out of the mold.
6. Pin up sides of mold with hat pins placed in opposite directions.
7. Heat up wax in double boiler or crock pot. Do not allow it to boil. Make sure no water is in the wax.
8. Pour wax, (melted at 212°F or below) into corn mold. Pour out excess wax when wall is 3/4" thick.
9. When wax has cooled, remove from mold Wax Corn on the cob. Wait till wax is very firm on inside, at least four hours unless quite cool environment.
10. Remove from mold and pour another corn. Repeat until four corns are cast.

OR

Cire Perdue Corn Positive à la Alginate Mold

Wax Corn a la Alginate mold: very immediate, can cast organic material, will not irritate skin, more detail, very tear able mold, harder to handle, will shrink and distort in several days, needs refrigeration. Several types of alginate are easily available, but none are inexpensive materials: Dental Alginate, Dermagel, Hydrogel N.

Ingredients and Equipment
One cob of corn with a hole drilled through stem and threaded with string
Razor blade and 20 hat pins
5 cups bees wax or Brown Victory wax, enough for four corns
Pot to melt wax in: double boiler, crock pot, preferably with temperature controller
Pouring cup for wax
About 4 cups Dermagel or other preferred brand
Bowl to mix alginate
Water and measuring cup
Plexi tube hinged on side or mold made from plastic containers and duct tape

Steps
1. Attach cob of corn so it can hang securely from hook inside the plexi cylinder or plastic mold. Allow about 1 1/2" clearance on all sides.
2. Start wax heating.
3. Check volume, measure enough Dermagel in bowl to fill the volume and add water to creamy consistency. One part to 1-1/2 part water or the proportion listed in the alginate you are using. Alginate will stay lumpy.
4. Mix fast with hands and pour into mold. Let set about ten minutes.
5. Open mold and cut down the side of alginate just enough to pull out corn cob.
6. Pin up the side with hat pins and pour wax into corn mold. Pour excess wax out when wax wall is at least 3/4" thick.
7. Remove wax corn from alginate mold and pour as many as possible until mold breaks down.
8. Store Alginate mold in refrigerator, good way to cool wax.

Sources
-Hydrogel N Polytek, 610 559-8620
- Dermagel: Douglas and Sturgess, Inc. 1888-ART-STUF www.artstuf.com
-Victory Brown Wax www.Fremansupply.com

Measuring amount of glass needed for glass casting mold
Once the wax positive is made, and before putting any mold material on the wax corn, calculate the volume of the positive by submerging the wax in water jar, and calculating the volume of glass needed by water displacement. Record that volume for use in calculating the amount of glass needed to fill mold. If using frit, specific gravity of the displaced water can be used to calculate weight of glass to be used. Add 1/3 more glass if using flower pot drip method.

Glass types
Either solid glass or frits may be used. The tinted Bullseye transparent yellow is perfect for corn. A mixture of clear opaque and transparent frits will give a more mottled corn effect, and have less transparency.




Wax positive and starting to apply Mold Mix 6

CAST GLASS CORN MOLD RECIPES
Two glass casting molds: Mold Mix 6 and Plaster/silica/refractory mold

Mold Mix 6 glass corn mold with flower pot drip fill
using glass billets

Mold Mix 6 is a high alumina shell material used primarily for casting metal. It can be applied with little mess, is excellent for small solid shapes like corn, and gives the glass a shiny surface.

Ingredients and Equipment
Wax positive
Latex or vinyl gloves
OSHA approved mask
Hair spray
Food coloring
Wood board 4"x4"
Metal grid
Pan of water to catch wax:
Mold Mix 6 (Luminar) 2 cups in sealed airtight container
Second airtight container to put half of the MM6
Open mouth glass jar with 1cup water, for washing brush
Stiff brush 1/2 ", not nylon.
6 cups beach sand
Braun hand blender
Propane and blow torch
Kiln furniture
4" flower pot
6-7" flower pot
High temperature gloves
Bullseye Glass tinted billets: yellow, a little less than one half billet per corn

Steps
1. Touch up the wax corn positive so surface is exactly as desired and construct a 2" x 1" reservoir out of wax and attach to the stem. Calculate the amount of glass needed to fill the corn mold. If using Bullseye tinted billets, do this by replacing same volume of wax corn with volume of glass. Then add 1/3 more glass by volume to account for glass left in flower pot.
2. Attach the wax positive reservoir to a wooden board so it stands up and can be moved around easily. Very important to attach it securely so it will not break off in the mold making process, which takes 3-5 days. Spray with light mist of hair spray.
3. Whip up about 1 cup of the MM6 in a separate seal able container with Braun hand blender.
4. Start to paint onto the wax corn, being careful to apply thinnest layer possible, and let dry until hard. MM6 is
inherently lumpy, so just work with the lumps to create a smooth paper pulp like surface.
5. Continue applying layers of MM6 every day until 4-6 layers are applied. Total thickness will be no more than 1/2".
6. Each layer may be colored with a little food coloring to distinguish layers. Make sure the layers near the
bottom reservoir lip are even and at least 1/2" thick. Do not apply next layer until first is dry. Keep layers as
thin as possible
7. When mold is hard and dry after last coating, take mold off the wooden board and set on metal grid over a pan of water. Best to do outside with good ventilation. Victory wax will burn with sooty deposit.
8. Use large propane hand torch, the kind used in a hot shop, to start melting out the wax.
9. Slowly heat the bottom near the reservoir so the wax begins to melt. Do not start at the top of the mold because the wax will seep out through the MM6. As it is heated, the mold will turn black and sooty. Try to avoid setting the
wax on fire by holding the torch far away. Continue to heat from bottom up. Melting process may take up to
half hour.
10. Slowly move up the mold and melt out wax from bottom of mold near the opening. Beeswax melts out more easily and has fewer fumes than Victory Brown wax, however it is more brittle to work with and a little bit more of
a challenge to touch up.
11. When wax is completely melted out of mold, increase the heat and torch the mold until it is red hot and turns from black to white again. It will then feel like egg shell. Let cool. Hold up to a light and check for cracks. Patch with another layer of MM6 if necessary. It has not been necessary to reheat with the torch after patching.
12. Pour thin solution of Bullseye shelf primer into MM6 mold with quick motion, fill it up and pour out immediately.
Pre-fire mold to 600F if filling with frit for firing. If using flow pot drip method, the pre-heat is not necessary.
13. Prepare 4" flower pot large enough to hold the glass and use pliers to grouse out the hole in bottom to make sure glass can flow easily. Place glass in flower pot.
14. Place mold in large 6" flower pot and fill with sand so sand is around the entire mold to be filled
15. Build structure of kiln furniture (can slice up broken kiln shelves into 1" strips) so that flower pot is about 1" higher than mold and hole is directly above the hole in mold. If the reservoir is at least 2" diameter, there is plenty of room for the glass to flow down in a circular movement and fill the mold. Do not support the flower pot on the mold, make a scaffolding of kiln furniture.
16. Start firing. When mold has reached 1550F for one hour, check to see if glass has filled mold. If not, maintain 1550F temperature until filled. Spoon more glass into the hot flower pot while in the kiln if necessary. When glass has filled, bring down kiln quickly to annealing temperature. Pull hot empty flower pot when mold is filled, because, sometimes the stream of glass from the pot will cause cracking in glass as it cools.
17. Cool and wait 24 hours after removal from kiln. Break away mold off carefully. With shelf primer is applied to the inside of the mold, the glass usually comes off clean.

Sources
-Mold Mix 6 (formerly Luminar)
ZRCI
PO Box 489
Florida, NY 10921
845 651-2200 www.zrci.com
Temperature Controllers: Digitry Company, Inc. www.digitry.com
-www.bullseyeglass.com

Firing Schedule for both Mold Mix 6 and Plaster/Silica/Refractory Mold

step	Step Time	Temp °F
1	1 min	200
2	6 hr	200
3	4 hr	1000
4	2 hr	1000
5	2 hr	1550
6	3 hr	1550
7	1 min	1250
8	2 hr	1250
9	1 min	1000
a	1 hr	970
b	5 hr	920
c	1 hr	920
d	1 min	800
e	1 hr	800
f	5 hr 30 min	250

Plaster/silica/refractory mold with reservoir and frit firing

This is a type of mold that releases easily, is tough and has little cracking and flashing. Very soft dental plaster can be used for the first layer. It is harder to make than MM6 mold, but assures easy release and for more complicated shapes, is more applicable.

Ingredients and Equipment
Wax positive
Latex or vinyl gloves
OSHA approved mask
Hair spray
2 lb silica, at least 120 mesh, some finer
1 lb 30 minute casting plaster
Plastic bowl or bucket to mix
1 lb refractory cement: approx 60% alumina, any brand available.
Plastic wrap
Wooden board 5" x 5" approx.
Wall paper steamer
Pan with water to catch wax
Metal grid to hold mold while steaming
Aluminun foil
Bullseye Frits: #1 or #2 clear with no more than 10% opaque and transparent yellow powders mixed in when clear
glass is moist.
Bowl to mix frits and spoon or spatula
4 cups vinegar

Steps
1. Attach wax reservoir to wax corn so it is very stable. Very important part, because frit will be loaded into reservoir when kiln is at1550F.
2. Attach wax corn and reservoir to wooden board and spray with Hair spray
3. Mix 1 part plaster and 2 parts silica 40% to 60% and sift into 1-1/2 part water.
4. Paint on first layer with brush, or use hands.
5. Continue to cover wax with plaster/ silica mixture until 1" thick all around. Let set one hour.
6. Mix up refractory cement with water so forms ball when squeezed. Pat over plaster/silica until a 1/4" to 3/4" shell is
created. May need to hold refractory in place with tin foil or plastic wrap. Can put hair pins in wax in order to control even thickness of the walls of the mold.
7. Pull out any pins before the refractory drys.
8. Steam out all wax from mold. When top of the mold is hot, usually all wax is gone. Use aluminum foil to cover mold and direct steam.
9. Let dry three to four days.
10. Set up in kiln so easy to reach and fill when hot. Use kiln furniture.
11. If using frits, measure glass and fill mold and reservoir. Turn on kiln and fire.
12. When reaches 1550F for one hour, check to see if mold is filled. If not, maintain 1550F and use large stainless steel spoon to fill until mold is full.
13. Cool and do not break out for 24 hours.
14. Break outside mold off carefully. Be careful when chipping away outside layer. Inside layer should crumble away. Soak in vinegar, then clean with water.

Firing schedule: See Above

Kilns
Top loading kilns with side and top elements work. Ideally kiln will have elements on top, bottom, and sides.

We both use Digitry controllers, have used them for many years, and find them student user friendly and good for our purposes.