Glass Lens Casting

[Friar1340]

New to The Melting Pot. Interested in working with someone in casting glass lenses for the collector car hobby. This is for just a few, not many (not production), both in clear and color. As an amateur machinist, I can fabricate patterns and molds, but need someone to pour. What material can be used for molds. I have access/use a dental plaster with an 18K psi rating and is used intended for molding precious metals so I know it takes heat. Can this be used? If not what is acceptable material for molds? Articles or references in casting appreciated. I'm in the NJ area. Chris

[BORO]

Look up "fused glass" on the web. A Good place to start

[Friar1340]

Having some success in slumpy into a two piece mold. There is detail on both sides of the pattern, hence the two piece mold. Firing at around 1425-1450. The mold material I'm using is dental plaster. The lower mold keeps cracking. I've read that some shops mix Wollastonite, Alumina Oxide or EPK Kaolin at about a 50/50 ratio to the plaster to give the mold more integrity. Drying out the mold at temps around 700 or higher to drive out moisture also helps the mold from cracking. All three test firings were configured with the bottom mold on the base of the kiln bottom. Would raising the mold up onto kiln blocks to allow air to get under the mold be better? Any suggestions?

Chris

[Joe Userton]

Having some success in slumpy into a two piece mold. There is detail on both sides of the pattern, hence the two piece mold. Firing at around 1425-1450. The mold material I'm using is dental plaster. The lower mold keeps cracking. I've read that some shops mix Wollastonite, Alumina Oxide or EPK Kaolin at about a 50/50 ratio to the plaster to give the mold more integrity. Drying out the mold at temps around 700 or higher to drive out moisture also helps the mold from cracking. All three test firings were configured with the bottom mold on the base of the kiln bottom. Would raising the mold up onto kiln blocks to allow air to get under the mold be better? Any suggestions?

Chris

How long and how did you dry the mold before firing?

It looks like your bottom is thicker, which could make it take much longer to fully expel moisture than the top, which could easily be enough to cause the cracking.

[snoopdog6502]

Molds that are too thick will break. I own a bunch iv bought and they are not thick for a reason. Mine are more like an 1/8"-3/16" thick overall.

They will dry better being thin too.

[menty666]

Try mixing in fine mesh silica (order from ceramics supply). Just make sure to use a n-100 respirator and good ventilation.

[Jackass Glass]

neat!

[Friar1340]

I thought this was worth sharing with the group. Latest results making molds to do slumping and found that a mixture of Dental Plaster (Rock Hard brand) and Wollastonite at a 50/50 mixture by weight seemed to work best. I also tried a mix of Die Keen (Green) Dental Plaster and Aluminum Oxide at a 50/50 mixture also held up for the most part. Dental plaster is available from
several sources such as the Plaster Guys (plasterguys.com and Ebay) and the Wollastonite from The Ceramic Shop in Philly (www.theceramicshop.com/), available by the pound. This does not mean that other plaster types/brands couldn't be used, but so far dental grade is working. FYI, there is also a mineral called Kaolin (some call it EPK) that is a clay based material that could also used, but I have not tested it (molded with it, but didn't run it through the kiln). Also available from the Ceramic Shop, by the pound. Would suggest thinning he mixture ratio to about 70% plaster and 30% Kaolin instead of 50/50.

Pic caption: On the left is the Die Keen & Alum Oxide. The small piece that broke off occurred when the glass was being pulled from the mold. On the right is the Rock Hard & Wollastonite mix.

[BurntHands]

Interesting work, thanks for sharing. Are you using an original plastic or glass piece to make the molds or did you carve them or mold around a plug you carved? 96coe furnace glass?

[BORO]

+1

O.P. follow up.