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I need help here. I currently use a round ring like mold made of 50-50 no.1 plaster and 200 mesh silica with chicken wire embedded to cast my telescope mirrors. I am experimenting at 2100 degrees. I don't need fine detail in my mold. I would like to strengthen my molds and decrease cracking. Can I add any thing to my recipe to improve my molds? Portland cement maybe? Refractory mortar of some sort? Or do need to throw my recipe away?
Ron

First, stop using chicken wire at any temp. Every time I've tried it I've gotten chicken wire-patterned flashing. Second, plaster isn't made for those temps. As I mentioned in the other post, talk with R&R or Remet about the slurry systems bronze foundries use, or have ceramic or special refractory forms made.

Another option would be to get a furnace heat the float to the melt point, and pour it into sand casts. If you search on YouTube you'll see examples of this.

It's possible that you'll find it cheaper and less trouble to simply switch glasses.

I gave you a reply in another post about using stoneware or porcelain paper clay that you can fire up to 2372F/1300C and use without kiln wash/separator but you completely ignored my post.

Peter Angel wrote:I gave you a reply in another post about using stoneware or porcelain paper clay that you can fire up to 2372F/1300C and use without kiln wash/separator but you completely ignored my post.

...or you can use stoneware or paper clay (and I still haven't tried using paper clay yet, Peter, I need to try it.)

Peter Angel wrote:I gave you a reply in another post about using stoneware or porcelain paper clay that you can fire up to 2372F/1300C and use without kiln wash/separator but you completely ignored my post.

Peter
I Apologize I missed it. I am intrigued. Please enlighten me. This is new territory for me
Ron

Morganica wrote:First, stop using chicken wire at any temp. Every time I've tried it I've gotten chicken wire-patterned flashing. Second, plaster isn't made for those temps. As I mentioned in the other post, talk with R&R or Remet about the slurry systems bronze foundries use, or have ceramic or special refractory forms made.

Another option would be to get a furnace heat the float to the melt point, and pour it into sand casts. If you search on YouTube you'll see examples of this.

It's possible that you'll find it cheaper and less trouble to simply switch glasses.

Morganica
I will try to call R&R today. I missed them yesterday. So far the plaster silica with chicken wire had gotten the job done for me despite significant cracking. Things like iron discoloration , cracks in the mold which is nothing more than a containment dam, and devit on top for me are no more than a nuisance. I does mean extra work for me. I do want to improve the quality of my molds though. Maybe even get something that is reusable. I don't know enough about furnaces yet and no one around here had one so I am kind of on my own
Thanks for your continued help
Ron

Have you ever thought of looking into these product lines . I know we hot poured into full sized head molds at a Residency at Pilchuck Glass School in 2005. We used to use the MM6 alot but I am now working in colour bars and not working with the product as much but OH it had such great possibilities. You can get a mold made that is not cheap BUT if used properly can last for years. (if NO undercuts which you would NOT have. Soooo food for thought . Give Mike Cauda a call. He represents the glass community and helps out greatly. mcauda@zirci.com I believe. Les
http://www.zrci.com/

ZIRCAR Refractory Composites, Inc.
P.O. Box 489
Florida, NY, 10921 USA
Phone: (845) 651-2200 Fax: (845) 651-1515
email: sales@zrci.com

Les, I agree that Zircar's a good place to look, but the problem isn't so much the mold as the release at prolonged temperatures of 2100F or thereabouts. MM6 might hold up, but I'm not sure I'd trust either kilnwash or most of the BN sprays I've tried, not for lengthy firing cycles. Hot pours are a bit different--you're out of the worst of the heat fairly quickly and you're not asking so much of the release.

I'd like to do some experimenting with paper clay under normal casting conditions, see if that works.

That would be wonderful Cynthia. My kiln does not go hot enough for testing . 1700 hundred is all I can do.

Morganica wrote:Les, I agree that Zircar's a good place to look, but the problem isn't so much the mold as the release at prolonged temperatures of 2100F or thereabouts. MM6 might hold up, but I'm not sure I'd trust either kilnwash or most of the BN sprays

I'd like to do some experimenting with paper clay under normal casting conditions, see if that works.

Have you had a chance to see if if it works? Also, where did you buy the porc.paper clay?


Thanks much!