Centering glass when draping

[Geo]

I am draping over a stainless steel bowl, and firing in a front loading GL24 kiln. I'm having trouble getting my glass perfectly centered before firing. Any tips?

[Morganica]

Personally, I think that's the problem with front-loaders; you can't easily reach most of the work. I've tried casting in the GL24 and it just about drove me crazy.

The best way I've found to work slumps with a front-loader is to literally draw your centering points on the UNDERside of the glass, then position the glass from underneath. (Obviously, this method only works for draping molds) By that, I mean put the flat blank on your worktable, upside down (so that the bottom is facing up). Position the slumper exactly the way you'll want it in the kiln, and carefully outline it. Then draw arrows pointing to the left/right/front sides of that outline, with great big wings (or whatever they call the diagonals on an arrow).

Put the slumper in the kiln, put the glass on it and eyeball the position. Then get down under the glass--use a flashlight if you need more light--and slide it until the points of all three arrows are visible and you can just barely see the slumper outline you drew.

The problem with this method is the marker--I use Sharpies, and every so often the mark seems to fire into the glass.

For regular slump-into ceramic molds that need special centering (most are pretty obvious), I put the glass in the mold before I put it in the kiln.

[Geo]

Great idea about the outline and arrows! Thanks so much.

[Marian]

Hang a weighted plumb line from the top of the kiln somewhere convenient- mark the center of your mold, place that under the plumb, mark the center of the glass, place that under the plumb line- should be good to go.

[Valerie Adams]

I wonder if marking with a little paper label would work instead of Sharpies. The label should burn away completely. Or perhaps a bit of tape, since I know that burns away.

[Saracen]

I've just bought a new kiln that is top-firing, and also not as deep as I thought, so how close to the heating elements can I place the glass I want to drape without causing any damage to my piece..or maybe even my kiln?

[Stephen Richard]

The cheeky answer is try it an see.
A possibly more helpful answer is to indicate that the closer you get to the elements, the slower your rate of advance needs to be. This is because the elements will heat the glass more in the areas directly under the elements. But there are lots of variables.
I have fired pieces 30mm from the elements, with a very slow rate of advance successfully.

[Bert Weiss]

If you draw an equilateral triangle, with the base (inverted) being the distance between elements, the space below the point is where the heat evens out. So, any closer than that, and you must slow down to compensate for uneven heating. The quick calculation is to use a depth equal to the distance between the elements. That is a more conservative calculation.

Many bowl shapes will yield a wrinkled drape over. This can be lovely or really awkward.

To center a piece on a mold, I usually use a straight piece of something handy and my fingers. I push the straight object in until it touches the mold, and place my fingers at the edge of the glass. When you can go all around and it is the same, you are centered.

[JestersBaubles]

If you draw an equilateral triangle, with the base (inverted) being the distance between elements, the space below the point is where the heat evens out. So, any closer than that, and you must slow down to compensate for uneven heating. The quick calculation is to use a depth equal to the distance between the elements. That is a more conservative calculation.

That's good information that I don't think I've ever heard before. Thanks! Dana

[haleybach]

If you draw an equilateral triangle, with the base (inverted) being the distance between elements, the space below the point is where the heat evens out. So, any closer than that, and you must slow down to compensate for uneven heating. The quick calculation is to use a depth equal to the distance between the elements. That is a more conservative calculation.

That's good information that I don't think I've ever heard before. Thanks! Dana

That is exactly what I was going to say.
Very useful and easy to understand information! Thanks