I've seen some concerns over melting temperatures of glass. While most are in the range of 1700 C, a hydrogen/oxygen torch can be reach 2000 C, and as he brought over a generator, it should be possible to electrolyze water for the oxygen and hydrogen. The hydrogen can be burned in air for a similarly high temperature.
There are several types of glass. Borosilicate is a mixture of silica and boron (B2O3) which had good thermal properties and is easier to make clear, though needs higher temperatures. There's also Soda Lime glass (mix of Na2CO3, CaO, sometimes magnesia, and alumina). How To Make Everything has a whole series of videos on his quest for clear glass)
One thing to keep in mind is that glass cools unevenly, so you have to anneal the glass at about 580 C to reduce stress in the final product.