Walls of drop mold vase very thin

[JeffP]

This is my very first attempt at using a drop mold.
The mold was created out of fibreboard. A simple square with a square hole.
I prefused 2, 3mm pieces of glass, which from research was right for a drop of 100mm (4inches).
The drop was quite slow and took about 2 hours.
Did I drop it too much as it did bulb out a little on the bottom?

[Brad Walker]

I would have used three 3 mm layers of glass, not two. Two layers for first two inches of drop, one layer for each two inches after that.

[JeffP]

Brad, I tried 3 layers and it was still very thin. Could it be that the glass is too close to the elements?

[Brad Walker]

What firing schedule did you use?

[Morganica]

Well, if the glass gets so thin on the side that it splits open, you have at least one of three issues: Too much heat, too fast heat, or too little glass.

Fortunately, it's pretty easy to figure out: Go look to see where the glass went.

If it's that thin all over, you simply don't have enough glass in your drop set-up, and as Brad says, you need thicker glass. A drop ring actually needs a LOT of glass; you're not filling the diameter of a circle, you're covering the surface area of a cylinder that needs to be a certain thickness (at least 3mm, probably), plus its base (the bottom of the piece). It can be surprising how much glass that takes.

Without knowing the size of the opening it's tough to tell if you had enough glass or not.

If you've given it too much heat, you'll have a bulbous or even folded base, so most of the glass will be on the bottom of the piece. The heat didn't stop in time, and the glass just kept following gravity down. If it keeps going long enough you'll be left with a ring of glass on the drop ring, and a nice, thick mound on the bottom of the kiln.

If the heat is too fast, the ring is insulating the underside of the outer glass and keeping it stiff, while the adjacent glass is heating up and starting to sag much sooner. It will begin to pull down first and the weight of the glass will keep pulling it down and stretching it out before the rest of it catches up. The glass in the center will be pretty thick, and get progressively thinner as you move up.

More than likely you've got some combination of all three.