Glue Placement

Many people use glue to hold their arrangements of glass together to get it to the kiln. There are many kinds of glue that can be used. It is best to avoid resin based adhesives, but most other kinds of glue can be used – including hair spray, lacquer, super glue, CMC and PVA in addition to the proprietary fusing glues. The cheapest with the fewest additives seem to get good results.

Remember the glue burns away long before the glass becomes sticky, so if the glass won't stay in place while you are assembling it, it won't in the kiln either. The glue is only to keep things together while being transported to the kiln.

But this note is about were to apply the glue you choose to use.

The glue should always be used in minimum amounts. If it is a strong water based glue, such as PVA, it can be diluted with water and still provide sufficient adhesion. The glue should be runny, not thick or a gel. Unless the adhesive is a spray, a small dot at the edge of the piece to be glued will be sufficient. Capillary action will draw enough glue under the piece to stick it to the base glass.

If you are spraying the adhesive, that should be done at the end of assembly, to avoid flooding the base glass with adhesive. It is often best when using these lacquer based adhesives to spray a small amount of liquid into a container and use tooth picks or other pointed implement to dot the lacquer at the edge of the pieces to be attached. This way you can glue as you assemble rather than waiting to the end.

Adhesive under the middle of a piece of glass is likely to give black marks and even large bubbles, as the combustion gasses cannot get out from under the glass. So always confine your glueing to the edges of the pieces. A dot at each end is all that is required.

Super Glue

Super Glue

by Morganica

There are multiple cyanoacrylates (superglues) on the market, and they will give very different results. Gel superglue formulations usually have some type of rubber or fumed silica additive to make them thicker, and the additive usually doesn't burn out. That's probably where the "superglue leaves a mark" originates. Usually the cheapest possible superglue is best for temporary glass holds because it'll mostly be additive-free.

The glue will burn out around 700F or so, so it shouldn't be used to position the glass against gravity. I disagree, however, that it should never be used. I buy cheap superglue by the carton and use it in everything from temporary casting assemblages to making glass boxes for frit panels to tack-fusing. It is the best way I know to hold wobbly pieces in place until you can assemble the rest of the glass around it.

Some tips for using superglue:

• You are more likely to get whitish residues if you let moisture get to the superglue while it's drying, so keep the glass surfaces as dry as possible and don't put a superglue-assembled piece on a wet kiln shelf.

• Always try to put the glue under opaque or dark glasses, just in case something goes wrong.

• Use the smallest amount possible. Don't flood an area with glue and lay the glass on top - that will almost always leave too much glue on the glass. Instead, I assemble the glass and put a drop of glue right where the two glasses join. Capillary action sucks just the right amount of glue into the joint.

• If you wipe excess glue away with acetone, be careful about which acetone you're using. Some types (such as nail polish remover) can have additives that leave residues on the glass and make the problem worse. If the glue is in a readily accessible area, it is usually better to wait for it to dry, then peel it off the glass with a razor blade. Only use acetone where there's texture or something else that makes the glue difficult to remove. And in any case, don't worry much about removing superglue right on the surface--it will burn off.

• Superglue joints will NOT support the weight of your glass, i.e., never, ever lift your assemblage by a superglued-on piece of glass. Common superglue is actually a lousy glue for glass--which is why it works as a temporary hold.

Glues in Kiln Forming

Glues have two major uses in fusing. One is to stick things together after being fused (cold fusing). The other is to hold things together before fusing.

Holding things together while preparing the piece to be transferred to the kiln is a major use of low tack adhesives and glues. All of these burn off a lot lower than the temperature at which the glass begins to stick together. So, if you are gluing overhanging pieces, for example, they can move after the glue has burned off.  If you are assembling pieces that will not stay in place while you are putting it together, glue will not help get the final result you want.  If you are gluing to keep things stable while you move it to the kiln, you may find everything is ok.

However, glue tends to boil off if the temperature is raised too fast. During this process, the effect of the boiling will move the glass pieces that are most unstable. This also occurs if you use too much glue. You should only use as much as will stick the pieces together. Also too much glue leads to black spots and sometimes bubbles between the layers of glass.

The adhesives commonly used are the Bullseye product “Glastac”, Elmer’s glue, diluted PVA - or school - glue. All of these take varying times to dry and hold the glass pieces in place. So, a popular alternative is hair spray. This is a lacquer which dries almost instantly. It provides a thin film of adhesive and burns off in the kiln with no residue. You should use the varieties with no additives.

Glue most often leads to problems or unexpected results, so several ways have been used to achieve the desired results.

One way to deal with unstable components on small pieces is to make a large piece with a repetition of the design and cut it up after fusing in to the sizes you want.  Clean the pieces very well, and then fire them again to at least fire polish to remove any cutting or grinding marks.

An alternative to using glue, especially at the edges where the pieces are likely to move, is to use dams. My practice is to make the dams slightly taller than the unfired piece and line with fibre paper. I put 3 mm fibre paper against the dam, and thinfire against the glass. Both of these should be 3 mm narrower than the final height of the fused piece will be. This is to allow the glass to make a rounded edge as it will not be able to stick to the fibre as it sinks down to its final height.

Bullseye hot dams as an example of damming

Another alternative to using glue is to fire the piece upside down, so that the pieces do not have to be supported. This does require some planning and forethought. You can draw the design in reverse on thinfire, using different coloured pencils for the various layers to help in building the piece up in reverse. You then cap the assembled pieces with the piece that will become the bottom. Take the whole to a tack fuse. Then clean very well to remove any residues from the shelf. It is possible to sandblast and then clean to make sure there are no residues left. Of course this is not possible if you are using dichroic or iridised glass. Also note that iridised surfaces and thinfire do not get on well – there is extreme pitting in the iridised surface. 

Example of pieces glued and ready for the flip

 Once the piece is cleaned, fire again to get the desired surface texture.

Cleaning a piece after first firing

Glue chipping, 9

Glue Ratings

The glue used for chipping glass is generally called animal hide glue. Many companies sell animal hide glue, but to get the best results, you must use glue that has been formulated and tested for strength.

There are many grades available, such as:

80, 110, 135, 164, 192, 222, 251, 280, 315, 347, 379, 411, 444, 478, 512 jelly gram strengths

The three grades suitable for glue-chipping are:
5x (weakest) = 135 gram strength
4x (suggested) = 164 gram strength
3x (stronger) = 192 gram strength

Glue chipping, 8

Different Glue Weights

The main control over the chip design relates to the ratio of glue to water per area of glass.

140gms glue to 850 centilitres water per square metre is the minimum. The chip will be spotty or absent entirely.

425gms glue to 850 centilitres water per square metre gives the best results – a uniform chipping usually in a fern pattern.

570gms glue to 850 centilitres water per square metre gives a larger more iceberg-looking chip.

850gms glue to 850 centilitres water per square metre is wasteful and usually the glue is so thick the glass won't chip at all.

Experiment with the intermediate amounts to see what you get. Keep good notes of all the variables involved, so you will be able to repeat a pattern if you need to.

Glue Chipping, 4

Applying the glue

The glass should be clean and have a dam around it.

Cleaning the glass is important. If there is dust left from the sandblasting/grinding stage, the glue will not stick to the glass.

Place the glass on a level surface. The glass should be room temperature.

Pour the glue onto the glass in an even layer between 1mm to 3mm thick. If the glass is level the glue will flow to a uniform thickness on its own. You can tilt the glass from side to side to help the glue flow.

CAUTION: If your glue is too hot, it may shock the glass causing it to break, allowing the glue to run all over the place. Another reason to avoid heating the glue to a high temperature.

Glue Chipping, 3

Mixing the Glue

The 'type' or 'pattern' of desired chip design is dependent upon the glue to water ratio.

Generally the dry glue is combined with COLD water in a ratio of 3 parts water, 1 part glue. This is measured by WEIGHT - 1 oz. of glue to 3 oz. of COLD water per sq. ft. of glass. If your glass is 24"x24", this is 4 sq. ft. so you will need 4 oz. of DRY glue and 12 oz. of cold water.

Using metric measurements is easier when combining wet and dry materials by weight. 1 litre of water is 1 kg. So for 0.1 sq. metre (approximately 1 sq. foot) of glass you need 25 grams of glue to 75 cl of water.

After mixing let this mixture stand for about 1 hour to absorb all the liquid. It also helps to cover this container to reduce evaporation. This mixture will form a gelatinous mass.

Average Recipe:1 to 2 ounces of Dry Glue per sq. ft.
3 ounces of COLD water per sq. ft.

OR

285 to 570 grams of dry glue per square metre
850 centilitres of Cold water per square metre

Heat this mixture in the double boiler. Do not try to heat the glue container directly on a burner. This will stink tremendously. Slowly heat this mixture to 60 – 65C (140 - 150 F). It is important that you do not boil this mixture and that is stays between these temperatures. Use a sugar/candy thermometer to measure the temperature of glue. Stir occasionally. Heat slowly.