I have been a recycled glasd artist for over 10 years. I have made tiles, jewelry (beads and pendants), and loads of stained glass items all out of re ycled glass of various types. Anything over 1/2" in diameter will need to be annealed. I worry about javing a glass top for the kiln as it to will heat up, but it will only heat up on one side and that uneven thermal expansion will most likely cause it to crack. I would use a very small insulated kiln with a thick stainless steel plate for the top. Use a pyrometer from an electric kiln to monitor the temp. With your extreme temperatures the plate should heat what is inside without direct contact with the light. The best fusing kilns heat from the top anyway. Remember that when fusing glass you can't use different glasses from different sources because they won't have the same coefficient of expansion (look that up). If you want to combine different colors of glass bottles, the only way to do it is to crush the glass to sand size and mix it really well. That way the glass will all expand and contract evenly