glass stuck in casting mold

Help! I am somewhat new to fusing, but decided to venture into jewelry making by using frit in a casting mold. Despite liberal use (4 coats) of boron nitrate spray, when I took it out of the kiln, it was stuck fast to the mold (Holey wine glass form). Freezing it for 20 minutes didn't help, neither did wedging a knife blade between mold and glass and hitting the handle. (did break off the tip of my knife!). Is there anyway to salvage either the mold or the pendant? What about the other mold (3 margarita glasses with posts for holes) that I haven't used yet? How to keep glass from sticking in it? THanks for any suggestions from those more learned than I!

freezing it worked

I mentioned that I had tried freezing the stuck glass in mold for 20 min. I pulled it out of the freezer, tapped on the mold firmly and nothing happened. 15 mins later, my husband walked by, did the same thing, and the glass released intact from the mold. Yee ha!

Now... anyone know what to do next time so as to not repeat the experience?

BN Spray

Make sure you are  using MR97 boron nitride spray. I bought some High Temp 1800 once that was not as effective -- glass stuck to stainless and also ended up with hazing of the glass where it touched the mold.

Dana W.

Jester's Baubles Fused Glass Designs

RE: BN Spray

I had the same issue, first used Slide Hi-Temp thinking it was the same as MR-97. I still have a mold sitting with stuck glass, the holey pendant mold from Creative Paradise I believe. Bought a replacement mold and actual MR-97 for the second try and it worked perfect. I had never thought about freezing - just put that stuck one in the freezer now to see if maybe, just maybe that will work!


glass stuck in mold

I just took a project out of the kiln and it was stuck in the mold. I used MR 97 Boron Nitride according to directions on a Patty Gray 6" square mold. I fired it to 1500 and held for 20 min. Then followed Bullseye schedule for cooling. Several things happened 1) the stacked glass did not flow to fill the mold 2) the glass cracked internally during cooling 3) it stuck to the mold BUT I love the color combination. I just put it in the freezer and am hoping for the best.

glass stuck in mold

I just took the mold out of the freezer and tapped it sharply - several times-nothing happened. Does anyone have any other ideas?

Glass sticking in mold

I have done some tests with MR97 it works well but it is expensive and because it is expensive it bugs me when there is over spray. What I would like to see from ZYP coatings is the same formulation as MR97 in a mix yourself or premixed formula that we can apply ourselves like good old fashioned kiln wash. I use kiln wash for all my slumping and fusing and it works fine. I like the hotline product best because it stays in solution longer (you don't have to stir it as much). If you are fusing glass into a mold as opposed to slumping it in, probably better to use the hi temp kiln wash from Hotline. If you are using Bullseye kiln wash, you will have to make more of an effort to keep it in suspension so you can apply evenly. What I found works well for this is mixing up your kiln wash in a bucket and using an aquarium aerator (bubbler) to keep it in suspension.

stuck glass

Thanks for the info on using a different kiln wash. I do have some Bullseye to use up then will try your suggestion.

Things to try

First, Patty recommends (at least for her 8x10 mold) that you line the bottom with Papyros or ThinFire. That works really well, though you might feel it is redundant (but it works!).

With the pendant molds, I finally gave up :). (I don't do a lot of jewelry and I finally decided they weren't worth the involved process). They seem to always stick for me. One way I have found to get them out is to invert the mold (glass facing down) on a kiln post or two and refire to about... I think about 1000 degrees. The pendants will drop out typically, though a few times I had to get out the high temp gloves and whack the mold on the table to get them to drop out :). This inversion technique would work for the 6" PG mold, too.

I love Patty's molds. You do have to be careful after you have coated them with BN, that you do not touch the sides with your fingers or scrap it with the glass. If you place a sheet of paper in there, just cut it ever-so-slightly smaller than the mold and nip the corners so it lies flatly.

Dana  W.

Jester's Baubles Fused Glass Designs

stuck glass


what a great idea! totally logical that it would work. I will definitely do it - I may have scratched the coating now that you mention it. I did rearrange the glass scraps a couple of times. Because this glass had to flow somewhat, I thought it might tear and pick up the thin fire. I  will use it next time. Thanks everyone for the info. Bet

High Temp 1800

You are correct in saying that the High Temp 1800 does not work. (at least in a Holey mold). I talked to the folks at Delphiglass and they actually changed their product description of the stuff. I think I got lucky with the freezer trick, but will not risk my molds again until I get some MR97.

Stuck with molds

After ruining 3 molds with Hi Temp 1800, I dumped the remainder of that product in the trash.  At least I didn't ruin a $90 steel mold like another worker I talked to.  Do not use and save yourself a world of aggravation!


Glass stuck in molding....drilled hole in mold to release

Well, drilling the hole did the trick to release the glass in my double pendant mold. Im very new at this, but i am going to try using the mold again to see how it works. The supplied instructions with the new mold only said to use a separator in it, and i did just that with 4 coats of the Pro Primer kiln wash. Hummm, i guess that didnt work too well.





stuck glass

I use Kiln wash, and frequently have a problem removin a piece without damaging the piece, mold or both. Today I had a flash of brilliance! WaterPik! I went around the piece with the WaterPik at the highest pressure. After 3 times around I inverted the piece and tapped the back. It fell ut into my hand, no damage anywhere. (Sprayed water all over the bathrrom. Change of venue next time?)

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.