I have been working with slumping melted wine bottles for a few weeks now. It is a little more difficult than I initially thought. I am trying to perfect several different molds, bottle styles, glass thickness, glass colors, etc. Each seems to perform a little differntly when fired in the kiln. I have found when I fire flat bottles, I can fire at a higher temperature, but when I fire in a mold, the peak temperature is usually 50+ degrees cooler than when using a mold. I have also found that different colors are more prone to Devit (devitrification). Devit is a white milky type coating that appears on the surface during firing. There are many things that can cause devit including:
Firing too long or too hot
Holding too long in the "devitrification temperature range"
Types of glass
Color of glass
I have been using a spray solution of Borax and water which has helped.
I have alot more firings to do before I can say I am successful at slumping all types of bottles. I have however found 5-6 bottle styles and a firing schedule that works most every time. I am getting some of these flat wine bottles in stock. The other types of flat bottles (liquor, vodka, bourbon, beer, etc.), I will be experimenting with, and adding to inventory as I feel comfortable with a repeatable process.
Time to get back to the kiln for more testing...check back later!