Hi,
To reduce the volume of my 100mL spirit burners and avoid filling them with too much alcohol but only 50mL, I would like to make a slope and fill them with epoxy resin. Which product do you recommend? The spirit burners are made of glass and have an inside opening of 17mm, I have about 20.

Thank you for your help!

You may struggle to fill them with a conventional casting epoxy without breakage.  The resins and glass have a different rate of thermal expansion.  This means that casting resin into glass objects can cause the object to crack or break.  If the design is quite tough and thick, then you may get away with it as the resin cast volume is quite low so the heat may dissipate quick enough to not be an issue.  The resin I would try is our GlassCast 50 Clear Epoxy Casting Resin

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant