glass imprint on open casting and white scum

[Miriam Silburt]

I am new to the board and hoping you can help me. On my first open casting using 96 large coarse in a hydroperm casting of a baby hats and sock the glass has an imprint of the large coarse glass pieces (very distracting!). The second issue is the white cloudiness on the glass even after scrubbing with vinegar. Looking for explanation and advice on this problem. My firing schedule was as follows

Segment 1 100f to 2000F, hold 5 hours
Segment 2 100 to 1250, hold 1 hour
Segment 3 500 to 1470 , hold 1 hour
Segment 4 9999 to 960, hold 6 hours
Segment 5 10 to 800, hold 1 hour
Segment 6 50 to 100 , hold one minute

Thanks for your help.

[Morganica]

Soooo...where is the white scum, exactly? Most likely it's some kind of devitrification and will need to be coldworked off, but it's hard to tell without pictures and descriptions.

"Veiling," i.e., faint outlines of the chunks of glass, is kinda the nature of the beast if you place the glass inside of the mold. The glass doesn't move a lot, so when it softens and slides down, it tends to trap tiny amounts of air that turn into extremely small bubbles on the surface of the chunk. When the glass fully melts together, those bubbles tend to stay in place, outlining what used to be the chunk.

Veiling is exacerbated by whatever's on the glass. That means that if each chunk isn't absolutely sparkling clean, it'll trap whatever's on the surface as the glass softens. Dust, oil from your fingers, small crumbs of glass that again trap tiny bubbles, residue from cleaning solutions, etc.--any of it can be trapped, outlining the glass.

If your goal is continuous transparency, it's usually better to drip the glass into the mold from above, the way you would a pot melt. Most of the air and schmutz will be pushed out of the way as the glass flows into the mold, and you'll have a much more transparent casting.

[Miriam Silburt]

Sorry for so long it getting back, sick family member. Thanks Cynthia for answering me. It was disappointing to hear that the outlining maybe the nature of the beast. Would using billets work as it might show less lines being a larger size? Do you think my schedule was ok for this open casting using hydroperm? Do you have some suggestions on a schedule if I try the pot melt idea? What size Glass pieces should I use? Do you think the devit (all over the piece) was because of unclean glass or the schedule? Thank you. If I can figure out how to send pictures I will.

[Kevin Midgley]

Too much heat work as in too hot too long.
For the pieces you currently have, my suggestion would be to sandblast the surface to a matt finish and to hide the defects.
Somebody you know or the local cemetery monument place could do it for you for probably minimal cost if you ask nicely.