Mirror sandblasting notes

We discovered this great information one day when we were looking up sandblasting information on cuttingedgesandcarving.com and just had to share it with our readers.  This posting was made by Kerri, from Mayflower, AR, unfortunately that was all of the information we could find.    


If you are etching the back of a mirror you must also protect the front of the mirror.  You can use a clear or light colored tape or shelving paper while working on it, since there is nothing more frustrating than finishing a piece and turning it over, just to see it has been scratched or a corner chipped.  


I etch from the back. I also use vinyl most of the time. I have used Ultra Pro Blue with success also.

I blast at 25-30 psi. It is a fascinating process to watch the silver come off! 

I leave the vinyl on then paint (you don't have too, you can take the vinyl off..but for me that just adds another step where I take the chance of breaking the piece!) . You can paint with just about any type of spay paint. I have even used brush on acrylics. If you want different colors, just use masking tape to block off the areas that you don't want painted 'X" color and spray the rest. Let dry and put a second coat on it. Use light coats other wise it takes forever to dry. When you are ready for the next color, take the masking tape off and spray the next color. Don't worry about masking the area off where "X" color is, as it the second layer of paint will not show through the first. Once you are done, spray the whole area with black paint (matte or gloss it doesn't matter). This final coat tends to give a final finish and bring out the other colors really well. I think that in the hand painted sign world this final step is called 'backing up'.  


The pic shown below is from Kerri, who posted it on the  Cutting Edge Sand Carving webpage.

  

Sandblasting resist types and sizes

One of the most important decisions to be made in glass etching is which resist to use for a specific job. What you are looking for is the least expensive resist that is adequate for the job at hand. Controlling costs is essential for making a profit, but you can go overboard.

In your zeal to keep costs low, if you use a resist that is too thin, you run the risk of ruining the project if the resist blasts off before the project is finished. This means you will have to start over after you put in all the time necessary to transfer the design to the resist and cut the design out for blasting. The wasted time will cost you much more than better resist would have in the first place.

If you always go for overkill and use only the heaviest resists available, you will not only be wasting money but it will be much harder to get the special effects you want. Since the heavier resists are thicker it is difficult cutting and blasting in fine detail. It is also more difficult to achieve subtle changes in depth when carving in small areas or subtle changes in gray scale when shading.

Consequently, it is best for the quality of your etching as well as the quantity on your bottom line to use the proper resist for the job. Know which resists are available and how to use each one of them to best advantage.

Resist Selection Table
Resist Type	Thickness	Uses	Characteristics
Clear Vinyl	4 mil	Shading to surface Etching	Adequate only for light Blasting, somewhat difficult to remove from large areas of glass without tearing.
Clear Vinyl	8 mil	Shading, surface etching, light carving	Good margin of safety for all types of blasting through light carving; does not tear when removed from large pieces of glass.
Clear Vinyl	11 mil	Light to medium heavy carving	Somewhat difficult to cut because of thickness, good for correcting mistakes in carved areas.
Opaque Vinyl	4 mil white	Shading to surface etching	Adequate for light blasting on smaller pieces. Difficult to remove from larger pieces without tearing out in strips.
Opaque Vinyl	6-8 mil white	Shading to light carving.	Inexpensive multi-purpose resist, easy to remove from glass in large or small areas.
Opaque Vinyl	10-15 mil white or black	Medium carving.	Thick, hard, difficult to cut. Good for medium carving.
Rubber	11 mil green	Surface etching to medium carving.	Very easy to cut, especially fine detail; very tough for its thickness. Can be stretched around curved objects.
Rubber	18 mil tan	Light to heavy carving.	Very easy to cut, good for fine detail; best overall for general carving. Can be used on metal or stone. Good on curved objects.
Rubber	30 mil tan	Medium to heavy carving.	Easy to cut, moderately good for fine detail, tough; can also be used on wood, stone or metal.
Rubber	45 mil green or tan	Heavy carving.	Easy to cut, difficult for fine detail, very tough; also used for wood, metal, stone.

 

Types of Resist
Clear resists can be used for surface etching when you want to avoid the step of tracing the pattern onto the resist on the glass prior to cutting out the pattern. Just place the pattern under the glass with the resist on it and cut the pattern, looking through the resist and the glass to see the pattern underneath. Although this technique can save a lot of time, many don't like it because it is difficult to see when your cut lines are properly aligned over the pattern. The reason it is not used for shading or carving is that in both of those techniques, you peel the resist in stages an blast each stage separately. By the time you get to teh third or fourth stage, the discoloration caused by the abrasive on the resist has partially obliterated the cut lines, making it very difficult to see just where the pattern has been cut. When you can't see the cut lines on the pattern, it is nearly impossible to peel the resist out properly. Opaque resist is much better for stage blasting because the trace lines show up much better after the blasting has been started.

The 4-mil clear resist is used frequently to protect the back of a sheet of glass from being scratched during handling. Thicker clear resist is used in correcting mistakes by re-applying it to a blasted area. Since you can see the blasted pattern through the resist, it is easy to see where to re-cut the pattern areas to be corrected and to blast the affected area again.

Rubber resists are more resilient and easier to cut than vinyl resists. They are also much more resistant to failure from excess heat generated by the friction of blasting. These factors make them better resists overall than vinyl materials. However, the rubber resists are considerably more expensive and are not available in the thinner sizes. Therefore, vinyl resists are used much more for blasting large areas and where the etching techniques don't involve very deep blasting. Any time are etching a particularly expensive piece of glass (such as crystal or thick plate glass), always use at least the 18-mil rubber resist to guarantee that the resist won't peel up during the blasting and ruin the glass.

About Contact Paper
Many people start out etching glass using contact paper as a resist. This is a 5-mil think vinyl which is used as a shelf liner for kitchen cabinets and it works acceptably well for shading or for surface etching except for one major drawback. It uses a permanent type of adhesive which stays on the glass when the contact paper itself is removed. The longer the material is on the glass before it is removed, the worse the problem is. On small pieces of glass, it is not too difficult to clean off after etching is done. On larger pieces, the cleaning process can take as long as the actual etching process. The benefit of contact paper is that it is very cheap. You may want to try it out if you are on a limited budget and if you can complete the entire process in one day or less.

Conclusions
When you are just starting out, you may not know what type of etching you will be doing most, and you may not know which resists to stock. Four types of resist will cover almost anything that comes up.

A 50 yard roll of 6-mil white is essential because it is an all around resist that can be used for shading, surface etching and light carving. It is very inexpensive and you will probably be using more of this resist than any other. A 10 yard roll of 11-mil green rubber resist will take care of most carving in 1/4" plate glass or wherever you need especially fine detail.

You will also need a 10 yard roll of 18-mil tan rubber resist for deep carving in 1/4" glass or most carving in 3/8", 1/2" or 3/4" glass. For very deep carving in 1/2" or 3/4" glass, you can double the layer the 18-mil resist. It is a little more expensive to do that than use the 30 or 45-mil resist, but you won't need to do it very often.

The last resist you will need is the 8 mil clear, which you will use for correcting mistakes and possibly for surface etching on small projects. About 10 yards is a good starting amount.

As you do more and more etching, you will develop your own favorite resists for your particular technique and for the type of jobs you are doing. Just remember, using the right resist for the job will always save you money and time and will give you much higher quality results.

This information was compiled by Norm Dobbins who was an expert glass sandblaster and teacher.

Trouble shooting the types of cracks in a fused glass piece

Here a list of the major types of cracks in fused glass and some information about why they occur and how to prevent them.

Curved cracks across the middle of the piece.

Improper annealing causes this kind of crack. It will show up as gentle curves (sometimes as straight lines) that break the pieces into two or three pieces. Often the crack will curve sharply as it nears the edge of the glass. This kind of crack is the piece's way of relieving stress. The solution is to spend longer annealing the piece.

Cracks where two different glasses come together.

Glass incompatibility causes these cracks, which often show up as curved cracks around the edges of the two types of glass. The cracks can be very small or they can cause the pieces to break apart, but they will always be along the edges of the piece of incompatible glass. Conduct your own compatibility tests or use "tested compatible" glass to keep this from reoccurring.

Small, interconnected cracks (like a spider web).

These cracks generally extend from a single spot on the underside of the glass. They aren't usually severe enough to cause the item to split into pieces. Sometimes shelf primer will also be stuck to the underside of the glass. Most likely, this kind of crack is caused by glass sticking to the kiln shelf. A close examination of the shelf may even reveal small pieces of glass that are stuck to the shelf. The obvious solution is to scrap the shelf clean and apply fresh kiln wash.

Pie-shaped pieces, with smooth edges.

These cracks, which usually occur with such force that they split the piece into five to ten pieces, are caused by thermal shock. The edges of the pieces are often rounded because these tend to happen early in the firing cycle (around 300 to 500 degrees Fahrenheit) and the edges round during later phases of the firing. The cure for thermal shock is to fire more slowly in the early part of the heating phase. You might also try cutting very large pieces into smaller ones before firing. Finally, it's a good idea to peek in the kiln around 400 degrees or so just to make sure the piece is still OK.

Cracks that occur long after firing.

Sometimes a glass piece will just be sitting on a table when you hear a sharp ping. It might be quite loud, and perhaps there's a second (or even a third) ping. When you check it out, you discover that the glass piece you thought was beautifully finished has cracked. (This cracking can even be severe enough to shatter the piece, leaving the artwork in pieces on the table.)

The reason for this disaster is undoubtedly stress that has built up in the glass piece. Stress can come from many factors: improper annealing, thermal shock, incompatible glass, and even "normal" wear and tear.  Improper annealing is the most likely culprit. If you can access the firing log for the piece, check to make sure it was properly annealed.

If you used the same schedule you've always had success with, then perhaps this piece of glass was a bit thicker or larger than normal. Perhaps it was a different glass than you usually use. Perhaps your "normal" annealing schedule needs to be adjusted to anneal just a bit longer and slower.

For more excellent information visit the website, Warm Glass,  and their link here.

How do you make a stained glass window fit a frame?

Often stained glass artists are not taught how to fit a stained glass pattern (or window) in to a specific sized frame.  Typically artists will be asked to make a window that will fit into an existing frame for a friend or customer.  Both the foil and leaded techniques use slightly different approaches to accomplishing this fairly simple goal.  After reading our tutorial we hope you will feel much more confident in doing this!

To begin with, we will start with the foil method.  Now, if you have a frame that doesn't have any glass in it,  and you can easily move it around...  place the frame on a piece of white paper on a hard surface (the piece of paper must be larger than the frame), the front side of the frame has to be facing you.  Before doing so, prepare the frame by cleaning out any old caulk in the frame, if needed.  The paper can be plain or it can have your pattern mostly drawn out on it.  With a pencil,  trace around the inside of your frame, where it touches the paper.   Now you know the exact size of the interior of the frame you are using.  You can now draw your stained glass window to fit in that frame!  

Next we will discuss how to do this with a leaded window, or a foiled window with a zinc or lead came border.  First follow all of the instructions for the foil method as listed above.  Then measure the width of your lead came from the outer edge of the came to the interior side of the came where it touches the glass in your window.  Ok, what that means is, looking at the drawing below, measure from the outer area that is marked 9/32" to the interior section that says 5/32".   The area between the arrows, drawn below.

Once you get that measurement (it should only be a fraction of an inch), draw another new line completely around the inside of the first traced line, that will be the width of the measurement you just calculated.   Use the first traced line as your reference.   Now the area of your pattern will be slightly smaller than the original window opening, as to allow the width of the came you are using as a frame.

If you are using a frame like in a door or house window that you can't remove for this tracing process, measure the area where you intend to place the window.  Once measured, we like to draw our pattern about 1/32 to 1/8 inch smaller than the opening.  Keep in mind that if you are using a came border to follow our paragraph above.

We advise new stained glass artists to practice fitting a window into a frame before agreeing to do this for a customer.  

Pattern shears vs Sharpie marker for patterns

Why do people use Sharpie markers to draw out the pattern they want to cut, on their stained glass pieces?  This method is inaccurate and basically a waste of time!  We can see how a person can lay a pattern on a light box, lay a transparent piece of glass on top of the pattern and trace the piece onto the glass using a Sharpie marker.  But what happens when the piece of glass is opaque and impossible to see even when using the light box?  When grinding a piece of glass that has a sharpie marker outline, what happens when the marker accidentally washes off?  Do you have to guess at the actual shape of the piece?  Do you have to go back and forth fitting the piece and then grinding, until the piece fits?

The professional method for transferring stained glass patterns, to glass,  is much different than the Sharpie marker method.  And it is faster, easier, and more accurate!  So below we have written a step by step tutorial for transferring your pattern to your glass.  This tutorial is for making a Tiffany window, yet a lot of this information also pertains to making a leaded glass window.

Transferring your stained glass pattern to your glass pieces tutorial

Step one, make a pattern to the exact size desired and number all pieces.  For reference we like to mark what color of glass each piece is, even the type of glass being used on each pattern piece as well (we also advise you to somehow mark the direction that you want the grain to go, on certain pieces of glass that you will be using- we do this by drawing an arrow) .  Once you are done marking everything, make another copy of the pattern, also using plain white paper.  Computer paper works well for smaller pieces.


We like to use regular white paper that comes in a roll that you can buy at Hobby Lobby, Walmart and a bunch of other stores.  If eventually you want to make more windows with this pattern, you should make more than just two copies!  Don't bother making mylar patterns, they are unnecessary.  We like to take our patterns to Kinko's to make our copies.

Step two, cut out all pieces on one pattern copy.  Save the uncut pattern to use later.  To cut out the pieces you MUST use either a pair of foil shears or lead shears, depending on what you are making, NEVER use regular scissors.  You can purchase pattern shears at most retail stained glass stores.  Never mix up your shears and use the wrong shears when constructing your window, because the pieces won't fit properly!

Step three, use rubber cement to glue your paper pattern pieces to your glass.  Make sure to pay close attention to the direction you want to follow on the glass.

Step four, cut and grind pattern pieces.  To confirm that the pieces fit properly, lay your ground pieces on top of the original uncut pattern to ensure correct fit.  Do not remove the glued on paper pattern until all pieces are ground and laid on top of original paper pattern.

Step five, remove and foil each piece, one by one, only after removing glued on paper pattern, and cleaning with a dry rag first.

Step six, with all foiled pattern pieces laying on original uncut pattern, tack solder pieces together.  Once done, solder all pieces.  Flip the window over and solder opposite side, then flip once again to make sure front side of window is still soldered nicely.  If not, touch up!  You're now done, add a frame, patina and clean and its completed.

Sandblasting Tutorial

We found this really nice older tutorial for sandblasting by Ellen Abbott  click here to see her blog and decided to share it with our readers today.

Sandblasting 101

I have been asked some questions in the comments of the posts about this job (previous posts 'working on paper', 'the next step' and 'starting fabrication') none of which I have answered so I thought I would do that now.

Alix asks...

How did you come to learn this wonderful craft?...Beyond watching a friend sandblast a crude stenciled rose on a piece of glass, we are completely self taught.  There was no instruction back then and so we just used the ‘trial and error’ method.    

Do you enjoy every stage of the work, or is it stressful?...I do and I don’t.  Doing the intermediate and full size art work is probably my favorite part.  I’d say the most stressful part (aside from deadlines) is the composition and design part.  It’s hard to get started sometimes.  I wander around a lot at this stage until I finally settle down.  The fabrication is just grunt work...cut the stencil, make the diagram, do the sandblasting, in this case cut the stencil again, do the cream etch and finally glue on the jewels.  A lot of steps but at that point it’s just technique.  I still like that part of it too.  I like the drawing part but I also really like the making part.

What happens if the glass breaks?

Have you ever lost a piece?...Well, you know, glass breaks.  It is unforgiving.  It’s doesn’t bend, it doesn’t absorb.  And so, yes, we have lost pieces.  I personally have not broken a piece in a very long time.  Nor has Marc.  But it’s not always in our possession.  Usually, if it gets broken, it happens during installation.  Twice we have lost a piece from having a suction cup fail.  One a nail clipped the edge when the molding was being put in.  But what can you do?  Getting upset does not solve the problem.  You just gotta suck it up and do it over.  And I hate doing them over.

steven (didn’t really ask anything) commented about 

breathing and holding the breath re precision....I too was in the unselfconscious habit of holding my breath while I worked.  I was scolded for this habit over and over so I have tried to learn to incorporate my breath as I work.  But sometimes I do breathe out for a very long time.

Now that the stencils are cut, they go through the sandblasting process.  Peeling the cut pieces of the stencil off in a sequential order, Marc sandblasts those areas as they become exposed.

Here’s the sandblasting booth.

Marc wears the air supplied helmet hanging by the door so he won’t breathe the dust.  The yellow tank on the wall is the filter for the air he breathes.  The small blue cylinder on the wall near the floor is a water trap to keep moisture out of the pressure pot (the metal tank with the green hose in the back) which holds the aluminum oxide he blasts with.  At the end of that green hose is the nozzle he points at the glass when he turns the system on.  It’s run by a large air compressor (not in this picture) and the air is piped in.  The square on the back wall is a filter in front of the exhaust fan.  The brown stuff all over the floor is the blasting grit.

Here are some details from the sandblasting process.

Here’s a little slide show that shows one of the panels from start to finish.  You might notice that the first 6 are upside down (that’s right side up to you).  He works on them right side up, upside down, sideways, whichever is easiest to get where he needs.  Most of this panel was done upside down.

I know that last picture in the slideshow, where all the rest of the tree is etched, it’s hard to see all the detail, but it’s just the photo, the glass all dusty.  The detail of the leaves will show up when it is cleaned off and held up to the light.

Now we have to prepare them for the background etching technique.

How to put kiln wash on a stainless steel mold.

Some molds, notably those made of stainless steel, do not always respond to the room temperature brushing or spraying techniques that are used with ceramic and other items. As a result, you need to heat the stainless steel mold in order to get the kiln wash to stick.

To do this, place the stainless steel item inside the kiln. Leave the lid or door of the kiln open slightly, just in case any fumes build up and need to be vented. Then heat the kiln to a temperature of about 500 degrees F. Control the kiln so that this takes about half an hour. Taking longer is perfectly acceptable.

While the kiln is firing, prepare your kiln wash materials. You'll need some kiln wash and either a soft, wide brush or a sprayer or airbrush. Lay the items you will need on a surface that won't catch fire if something hot is placed on it. 

You may use either a brush or a sprayer, but be aware that using a sprayer or airbrush on stainless steel molds will result in a smoother finish than using a brush. In addition, some artists also use a mask when mixing and spraying kiln wash. This keeps you from accidentally breathing in kiln wash particles, which can be harmful if inhaled.

Once the temperature in the kiln reaches 500 degrees, turn off the kiln. Put on your gloves, reach inside the kiln, and carefully remove the stainless steel item. Place it on the nonflammable surface, next to the kiln wash.

Spraying on kiln wash is a simple matter of applying a thin, even coat of kiln wash on the outside surface of the mold. The kiln wash will sizzle as it goes on. That's the sound of the water in the mixture evaporating and leaving the protective powder behind.

If you've decided to apply your kiln wash with a brush, make certain you've selected a brush that will resist the heat of the stainless steel. Foam brushes (and some haike brushes) will not work, but most good quality paint brushes can withstand the heat.

Quickly use the brush to apply the kiln wash. Cover all areas that might come into contact with the glass. As with a spray application, the kiln wash will sizzle as it goes on. Once the stainless steel item is covered with kiln wash, allow it to dry completely and return to room temperature.   If you wish, you can return the mold to the still warm kiln to help it dry more quickly, or you can just let it air dry.

One application is often sufficient to cover the stainless steel item. If not, simply reheat and coat again. You may want to sand lightly between coats. Once the item is dry and room temperature cool, check to make sure that none of the air holes at the bottom have been filled with kiln wash and are in need of opening.

Some people rough up the surface of the mold prior to applying kiln wash to help it stick better. If you decide to do this, use very fine steel wool (000 works well) and make certain you wash the mold well before applying the kiln wash.

When you finish, the mold should be smooth to the touch, with no visible gaps or bumps. The kiln wash application should last for several firings, but if it flakes away, starts to look thin, or discolors slightly, you should reapply the kiln wash. For best results, lightly sand the mold with very fine steel wool before reapplying.

Many thanks to the Warm Glass website for posting this important information.  Click here to read the Warm Glass website!