Removing Kiln Wash

Kiln wash can get stuck on items for a variety of reasons. 

A variety of ways to remove the kiln wash are:

Grind the kiln wash off with diamond hand pads, or small rotary tool with wet sandpaper. You can then proceed to continue to grind with successively fine grits until a polish is achieved, or you can fire polish after a thorough cleaning.

Example of scrubbing kiln wash off

You can sandblast off the kiln wash and then proceed in either of the fashions above.

You can soak small pieces in tri-sodium citrate and then if necessary scrub with a wire brush – a brass wire brush is preferable to steel one to avoid scratching the glass.

Another solution is to place small items in an ultrasonic cleaner basket with water and a little soap or proprietary cleaner. Leave for an hour or two and they should be free of the kiln wash.

A link to some methods of cleaning shelves is here.

Grinder Chipping Glass

There are a number of reasons that may cause the grinder to chip the glass surface. Some of the things to check are:

Too much pressure

It may be that you are pressing the glass into the grinder head too hard. The grinder head should do the work. Firm rather than hard pressure should be applied. If the grinder slows, it is an indication that far too much pressure is being applied.

Insufficient water supply

There may be too little water reaching the head to lubricate the diamonds and keep the glass cool. If you are getting a white paste or a powder on or near the glass, you need to increase the water supply.

Worn or damaged grinder bit/head

Inspect your bit carefully for smooth areas showing that the diamonds have been worn away. Also look for dents, and other irregularities on the surface, indicating that the bit is damaged. Any dents or smooth places on the bit cause a vibration that is similar to a tiny hammer tapping the edge of the glass.

Grit size

It is possible that you may be using too coarse a grit on the grinder bit/head. The more coarse the grit is the larger the chips will be taken off the edge surfaces. Smaller grits take smaller chips off the edges, and so are less obvious.

New bits

Examples of the range and grit differences in grinding bits

If it is a new bit that is causing the chipping, consider dressing it. New bits often need to be dressed – removing protruding diamonds, or cleaning and exposing new ones on a worn bit. To dress the bit you can grind some scrap glass, brick, or use a dressing stone to lightly grind some of the abrasive material away. This most often settles the bit and avoids chipping.

Cutting thick glass

Use the correct angle of cutter wheel for the thickness. 

Use a similar pressure to cutting 3 or 6 mm glass. It is natural to think that as the glass is thicker, you need to use more pressure. The different angle of the cutter wheel is designed to transfer the standard pressure more directly downward.

Use cut runners made for thick glass to help break the glass. Run score from both ends of the score, especially on curved scores.

Example of cut runners for thick glass

Alternatively, turn the over and use hammer and rounded screw driver to run the score (similar to tapping method for thinner glass). Place the screw driver blade directly over the score line and tap it with a hammer. This will start the run. Continue it by placing the screw driver over the score at the end of the open score and tap again to continue the run.

Air Brushing on Glass

Raphael Schnepf Workshop

Air brushing onto glass is a little different than onto other slightly absorbent surfaces. As glass cannot absorb the moisture from the material being sprayed, the medium needs to be allowed evaporate. This means that each layer of paint must be allowed to dry before the next layer is applied. If too much liquid is applied to the glass, it will bead up giving a stippled appearance to the finished result.

There are some things that can help to give an even application of the paint or enamels to the glass.

Clean the glass very well. After thorough cleaning and drying, use some of the paint to rub the glass. As the paint is a slight abrasive, it cleans off anything the other cleaning methods could not get off.

Add a drop of washing up liquid to the mixture of paint and medium (liquid). This breaks the surface tension of the medium and reduces the tendency to bead up on the glass.

Use alcohol part or all of the medium. This reduces the evaporation time. Also apply in a warm rather than cold place. You can use a hair dryer on low speed and power to assist the drying.

Apply in thin even layers, allowing the paint to dry between applications.

Open the air brush trigger before reaching the edge of the area to be painted and close it after reaching the other edge. Any overspray can be cleaned up as in any other painting.

A slightly larger opening at the nozzle is required on the air brush than for other paints, but you have to be careful to avoid opening it so large that you get the spitting of large drops of paint onto your surface.

Because you are putting very small particles into the air you need to observe various precautions. You need to have a dust mask on at all times you are air brushing. You should do this in a spray booth with extraction if possible. If not, you need a well-ventilated area and very good clean up afterwards.

Avoiding Large Bubbles

“I tried small projects and they turned out fine. I have a 12" square with an emblem in the centre and a border set in slightly from the sides. Most of the glass is only the one layer. Both firings produced huge bubbles in the areas where the glass was only one thickness.”

Scale does matter. What can be done at a small scale does not always transfer to a larger scale without alteration.

 

The first problem this project created was using only one layer as the base. Glass has a surface tension which means that it tries to become 6-7 mm thick, which is twice the thickness of a single layer. As it thickens at the edges, it traps the air under other parts of the glass, and as the glass continues to soften the expanding air bubbles come up through the thin parts of the glass.  Using two layers of glass with the design on top will ease the problem.

 

The design is the second problem. The weight of the border makes it even more difficult for the air to get out from under the glass.  Although having two layers of glass will reduce the problem, think about ways to make the border incorporated with the second layer of glass, so the weight of the glass at the perimeter is not greater than the interior.

 

The third problem is that there is not a bubble squeeze in the schedule (indicated elsewhere in the query). The soak of 10 minutes at 538ºC/1000ºF is not necessary. You do need a soak at a point between 620ºC/1148ºF and 677ºC/1250ºF - this is the bubble squeeze temperature range. It is also the slump temperature, so you can determine what the bubble squeeze should be for your glass by what the upper slump temperature is.

 

The bubble squeeze can be accomplished by a half hour soak at the slump temperature, or by a slow rise from 50C below the slump temperature – taking an hour or so, depending on the size of the piece.

 

A fourth problem is the that the separator is kiln wash, and the edges of the glass conformed to the kiln wash, resisting the movement of air from under the glass.

 

You may need to change to fibre paper for single layer pieces, as that allows more air out. Shelf paper may be enough, but you can also put it over 0.5 mm fibre paper for greater air release. Alternatively, sprinkle powdered kiln wash over the fibre paper and smooth it if you don't want to use Thinfire.

 

Lastly, try to avoid the factory set schedules in your kiln's controller, as they are generally set for 6mm thick pieces.

 

Look at the glass manufacturer's website. Bullseye, Spectrum, Uroboros, and Wissmach give basic firing schedules that work with minimal adjustment. I don't understand why kin manufacturers don't simply refer to the manufacturers’ sites to give their customers good advice, instead of the pre-programmed stuff.

Orientation of Cutter Heads

In addition to the alignment of the cutter, you need to be sure you are moving the cutter forward in the way it was designed. If you look at the cutter from the side you will see two things. The most obvious one is that the angles of the cutaway on the head are shallower at the front and steeper at the back. In addition if you look carefully, the axel for the wheel is slightly forward of the centre line of the whole cutter.

Cutters aligned to score to the left

So it does not matter where the fixing screw on the head is. It may be at the front or at the back. What matters is the cutaway at the back which allows the cutter to be used with a shallower angle, than if reversed. This is most obvious on wide cutter heads.

Cutters arranged to score to the right

Repair of a Plastic Barrel Cutter

Generally, there are two parts that can break or be damaged – the wheel and the barrel.

Wheel

If the wheel is damaged or worn, you can replace the head. When considering that, look at the cost of the head and consider whether the small cost difference indicates you should buy a new cutter instead.

The most common damage is a flat spot on the wheel. You can check for this, immediately after dropping the cutter, by lightly moving the cutter across a smooth piece of glass. If you hear a regular ticking sound, the wheel is probably “flat spotted” and will need to be replaced.

A worn wheel is more difficult to detect and is also much less likely to occur. I have been using some of my cutters for 15 years without any sign of being worn.

Plastic barrel

Sometimes the plastic barrel cracks or breaks. This will mean that the oil in the cutter will leak out. So you can consider continuing to use the cutter without oil, or by dipping the head in an oil soaked bit of cotton wool or similar material before each cut.

If the break is at the threaded end and you want to continue to use the ball at the end for tapping purposes, you can glue the barrel back together with an epoxy resin. Make sure the pieces are free from oil. Then glue and allow to cure. After curing, sand down any excess resin to make the cutter comfortable to handle.

Then for additional strength you can wrap with dental floss or extremely fine wire. Start below the glued area and go to the end of the break and back again. You could coat this wrapping with epoxy again both to secure the wrapping and to further increase the strength.

Another solution is to cut the cracked end off and re-thread the remainder. It makes the cutter a little shorter, but will continue to hold oil and give good service.

Or, you could buy another cutter.

Gas Fired Kilns

Installing a Gas Fired Kiln

There are a number of considerations about the location of a gas kiln.

Air exchange

The kiln should be placed in an area where there is good air exchange. For a number of reasons, it is usually convenient to place the kiln near an outside wall – ventilation and canister storage are the two most important.

Ventilation

There should be a low level vent to the outside to allow air to rise for the use of the combusting gas. There needs to be high level vent for the gas to escape. Ideally a hood with powered extraction would be installed.

Space

As with any kiln, you need to have sufficient space around the kiln to avoid heating any flammable materials. In the case of a gas kiln you need to be careful to avoid storing any thing that might ignite above the kiln. You can put heat resistant materials around the kiln if desired.

Location and storage of gas canisters

The safest place to put the gas canisters is outside the building. This does mean going outside to turn the valve on the gas canister on and off. However this is the safest place, should any fire start in the building, because the fire brigade can find and remove it from the fire. This placing applies to both the in use canister and any other full or empty canisters.

Detectors

Finally, even with these precautions, you should install a carbon monoxide detector. Carbon monoxide has no smell and can overcome you very quickly. Even a few minutes of exposure can leave you feeling ill for days.  

Paint and Cold Working

One of the difficult things in cold working is determining when it is time to move on to the next grit size.  You really cannot tell while the piece is wet, because the water disguises the minute scratches put into the glass by the grinding process.

After you have dried the piece, you can coat it with a white paint pen. It is not necessary to cover the piece completely in white pen.  The white marks will be taken away by the grinding to give evidence of where you have already ground the piece.

Piece prepared for the next stage of grinding

You must make sure the paint has completely dried, or it will wash off with the water used in the grinding.

I find I get best results from this "witness" by making the paint pen marks at right angles to the grinding direction.  When all traces of the paint have disappeared, you have thoroughly covered the piece with that grit size.  Being ever cautious, I tend to dry, paint and do a second pass at the same grit before going to the next finer grit.

Cold Working Holes

If you have, or expose, holes while cold working a piece, you need to keep the glass waste from settling into them. Dry the piece and with a bar of hard soap rub over the area until the holes are filled with soap. Then polish off the excess with a cloth or paper towel. 

The filled hole in this piece is the white dot half way up on the right side

When finished cold working, you only need to wash out the soap, which is much easier than trying to get rid of powdered glass.

Based on comments from Cynthia Morgan, posting as Morganica