Is Pate de Verre Watertight?

Clear frit sintered at 690C, 670C, and 650C (left to right)

"This is fascinating. I had no idea about the water leaving the glass at different temperatures."

 This comment was made in relation to some of my tests of pate de verre at different temperatures. I sintered glass at 620°C, 650°C and 690°C (1150°F, 1200°F, and 1275°F) to test for the strength of bonds at different temperatures and thicknesses.

 Because the glass appeared porous in some cases, I tested to see if vessels would be watertight at the different sintering temperatures. I found that at 620°C/1150°F the glass leaked water slowly. At 650°C/1200°F the water “sweated” out. At 690°C/1275°F it was watertight.

 It is not that the water leaves the glass. There is no water in glass. The question is whether the sintering is watertight at different temperatures. At the lower range, the sintered glass is porous; mid-range they sweat like unglazed pottery, but at the higher temperature they are watertight.

 Pate de verre is a form of sintering glass – normally in a mould. In pate de verre, a vessel needs to be fired at a higher temperature to be watertight. If a porous wall is acceptable, it can be fired to a lower temperature to preserve the granular appearance on the inside. The outside – which is in contact with the mould – will retain the granular appearance at all these temperatures. If the object is decorative, it can be sintered at a lower temperature which will preserve the brilliance of the colours.