I need to heat up curvy glass substrates up to 400-450 C. So these substrates are not like hemispherical flasks, more like watch-glass; less curvature and short in height. Do heating mantles supply heat via only conduction? Can I still get high temperatures via convection? If not so, do you have any experience/suggestion for thermally conductive medium (thermal sand, cement, paste etc.) to allow transfer of heat to the substrates from heating elements/tapes inside the mantle? Thanks!