WarmGlass.com

Can you answer a couple of basic questions for me about chads? All I know about them is you use them to avoid or minimize bubbles between layers of glass when fusing. How big/small should they be? And you place them at corners and maybe sides of the pieces you are fusing, but what happens to the chads? Do they melt and fuse I with your other glass? Does that distort the corners and edges, requiring cold working afterward to clean up the shape? If I want to fuse 3 layers of 3mm glass together, can I do it in 1 step (all3at once?) do I need to use chads, and if so, between all layers? Many thanks for your help.
PG

Chads..the smaller, the better.. I use approx. a 2mm.(1/16") length of clear stringer right at edge. Only 1 req'd for fusing round discs. If you get them too big you'll see them after fusing. I grind and polish all my edges so it's not an issue.

Great! Thanks.

I don't like chads; I've never used them without being able to see them. If you build your design so you can cut off the edges, that's an option.

But many people use a fine layer of powder between layers for bubble control:
http://www.bullseyeglass.com/methods-id ... power.html

I use them every so often and always have to cut them out after first fuse.

Barry

As the others have said, unless you can make them really REALLY small or plan to cut them off, they are obvious. I prefer the powder between layers method.

Instead of using chads you can use clear frit.

The problem with chads is that they change the volume of the glass at that point in the piece. If you're capping a 3mm sheet of cobalt blue with a 3mm sheet of clear, you've got a 1:1 ratio of blue:clear. If you add a chad, you no longer have that 1:1 ratio. If the chad is cobalt, it'll be darker blue at that point; if it's clear, it'll be lighter blue.

About the only place it won't show (much) is when you have a dense, opaque glass. Or you can work the chads into your edge design, which can be kinda cool.

But to answer your questions:

First, chads are mostly used to separate layers of glass, so that the softening glass will sag first at the point farthest from all chads (in the center of the sheet), and then slowly collapse out, pushing air out ahead instead of trapping it. You can also use them to position glass for slumping or fusing, so that it will settle into the right spot during the firing.

Size-wise, they should be only as big as it takes to do the job, so if you're just raising the glass up to keep air moving, as small as you can cut them. The exception would be if you can't cut off the chad in a spot with some decorative elements and don't want it to show; then you'd cut it the same shape but slightly smaller than the element on top.

Typically, you place the chads on the extreme edges of the top layer where the glass is liable to come down prematurely and trap air. You WANT the glass to sag in the very center but the edges to stay high until the last minute.

Yes, a chad will add volume to the glass, so the more heat you add to flatten out your fuse, the more distorted the edge will become. You either cut or coldwork the edge to bring it back into shape, but most people cut the original blank about a half inch wider than the finished piece, use the chads, and then trim the coldwork the edges back to the desired size before slumping and firepolishing.

Finally, under ordinary circumstances you shouldn't need to use chads for fusing; they're really only needed when you've got raised areas trapping air underneath the top layer of glass. If you do, you should review your firing schedule and layup techniques because you can probably make some changes that will help. In extreme cases, you can prefire your layers flat, then stack them together and fire again for the final flat fuse.

If you do need additional help in avoiding bubbles, the clear frit between layers works well. just be careful not to overdo it, or the excess frit can itself trap air and make bubbles.

Thanks for all the very helpful information. I understand the process much better now.

Chad? His friend Robert is much cuter.

Maybe so, but Chad gives me a lift.