Resists

Avoiding bubbles between the resist and the glass on large sheets when preparing etching or other resist based processes is often difficult.

A trick learned from the firms that apply advertising vinyl to vehicles is to use a spray filled with slightly soapy water.

Their process uses pre-cut vinyl with an adhesive backing. So the first thing to do is to pick out the unwanted pieces. That is the pieces covering the areas that will be etched. Then you need to put a backing onto the front surface of the picked out vinyl – usually really wide masking tape.

Lay out the vinyl on the glass. Tape one end of the vinyl securely to the glass. This ensures that you get the vinyl correctly aligned over the whole area. Fold the whole piece of combined vinyl and backing back to the taped edge.

Carefully peal back the covering for the adhesive side making sure you do not pull off any of the isolated vinyl pieces. Spray the glass with a mist of soapy water to ensure all the glass is covered, do not have the glass running with liquid, but be generous. Too much liquid means that there will have to be a long wait for the vinyl to be firmly attached to the glass.

Start the application process by folding the vinyl onto the glass. Use a credit card or better, a large squeegee such as used for grouting mosaics. The tool you use must be smooth to avoid scratching the vinyl. Push the soapy water forward and to the sides as you move along the piece of glass. Keep pulling the protective layer evenly off the adhesive side as you work forward.

When completely attached, remove the backing from the vinyl. This will enable you to see any bubbles you may have left. Work out any bubbles by further pressing the soapy water out from under the vinyl to the edges. Where any remaining bubbles are in the way of the design, puncture them and work out the bubble of moisture through the hole. Cover the puncture with a small piece of vinyl.

Leave for a day for the vinyl to become firmly attached to the glass and then you are ready to do the etching.

Where you are going to cut the vinyl by hand, you do not need the backing. All the rest of the process is the same.

Creating your own Iridescence

Often iridised surface details are created by using iridised sheet glass and then masking and sandblasting off the unwanted portions. But you can make your own iridised surface detail much more cheaply by using pearlised  mica powder.

One way to apply the mica in areas of detail is to make a stencil from stiff card and sift a smooth relatively thin layer of mica onto the area of glass you want to be iridised.

A second is to mix the mica and powdered clear glass in equal amounts and sift that onto the glass through the stencil. This can help more of the mica to stick to the surface. 

A third is to sift clear powder on first and then a coat of mica. This works less well for me than the other two.

It does not matter if you put too much mica on, as the excess will not stick and can be brushed back into your container for future use. The firing should be at full fuse temperatures to allow the mica to sink into the surface of the glass. When you have poured the excess powder off you are left with an iridised surface where the mica has sunk into the glass. You can, of course, use any of the coloured micas for this purpose.

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, 7

Variables Affecting Chipped Patterns
The glass chipping pattern is subject to many variables. The duplication and uniformity of each pattern is dependent on control of these variables.

There are many variables to be considered, The major ones are:

1. Glass - type and surface preparation
2. Room temperature during preliminary drying stage
3. Glue - type, concentration, and temperature at time of application
4. Weight of dry glue applied per area of glass
5. Dryness of glue film at end of preliminary drying stage
6. Temperature of drying room during chipping process

Glue chipping, 6

Secondary Drying and Chipping Stage

The secondary drying and chipping stage is when a small space heater can be used to warm the glass up to around 52C (125 F). Do not point the heater directly at the glass. Keep it at least one metre away from the glass. You don't want to cause the glass to get too hot and crack.

This indirect heat will cause a rapid evaporation leading to curling of the glue and the chipping of the glass surface. The glass is under extreme stress at this point and should not be handled unless absolutely necessary. On sunny days the glass can be set in direct sunlight. This is the easiest way to get the glue to chip the glass.
The chips of glue can pop off and travel some distance, so take appropriate precautions, i.e. safety glasses, gloves, aprons. You might want to place a cloth over the surface.

After all the glass is chipped, some glue may still be left on the glass. The glue is water soluble, so you can soak the glass with warm water and scrape off the softened glue. Be careful of the extremely sharp shards that are now concealed in the water.

The glue and glass shards left from the chipping process can create a big problem if not cleaned up. Because the glue is an animal by-product, cats and dogs love to eat this stuff. This can cause your pet extreme harm and even death! Dispose of the waste carefully.

Glue Chipping, 5

Drying time

The glue will go through an initial drying stage. This is in the first hour or two, depending on the humidity and temperature of the room. Make sure to keep the glass level during this period.

The next drying stage takes between 12 to 24 hours. This is where the glue will cure and loose almost all of the liquid. A fan to circulate the air will speed up this process. The glue should be left to dry at its own rate, do not hurry it by heating. Uneven curing may result in a poor chip pattern.

The secondary drying and chipping stage is when the glue actually starts to peel or chip. The glue shrinks considerably during the total drying process. As it shrinks, it grips into the pores caused by the sandblasting and literally rips the top of the glass off.

Use precautions when handling glass that has a dried layer of glue. Goggles, gloves, aprons are the minimum precautions against the slivers of glass.

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.

Glue Chipping, 2

Preparing the glass

The surface of the glass must be roughened up to allow the glue to adhere to the glass. This roughening is most often done by sandblasting the area of glass to be chipped. It can also be done by grinding the glass with grit between the glass to be chipped and another hand-held piece of glass. The grit should be at least 100 grit, and coarser is better.

After this roughening is done clean the glass thoroughly. Use raised masking tape to create a dam around the edge of your glass. This will keep the glue from flowing over the sides of the glass.

Glue Chipping, 1

Glue Chipping Glass is easier than you might think. All that's needed are a few materials and a little experimenting. You can chip on a variety of glasses such as clear, coloured cathedral or flashed glass. You can also chip bottles, jars and even mirrors.

The glue used for chipping glass is animal hide glue or "glass chipping glue" and can be purchased through most stained glass retailers and art shops. It should be granular and is usually sold by the pound. One kilogram will generally chip up to 2 square metres.
The basic steps are:

• Prepare Glass
• Mix glue
• Apply glue
• Let dry
• Clean with warm water