Drying Molds

Jack Bowman · Post by **Jack Bowman** » Mon Apr 21, 2003 11:14 pm

I thought I posted this once but it didn't show up so here goes again.

I took a 2 week casting class last year where we were using Gerry's Mold Mix. We fired in wet molds the whole time with no serious problems.

How do others usually dry their molds? Does anyone in here fire wet molds?

Thank you,

Jack

Carol Craiglow · Post by **Carol Craiglow** » Mon Apr 21, 2003 11:22 pm

Hey Jack....I fire wet molds all the time...that is I put the glass in when it's wet and dry in the kiln. I spend some time at 200F 6 - 12 hours depending on size and then go up slowly, around 200 dph, to 1200F.

I think it gives a better surface texture than completely dried before hand molds, for some reason.

Carol

Jack Bowman · Post by **Jack Bowman** » Mon Apr 21, 2003 11:42 pm

Carol,

That sounds pretty much like what we were doing. At times when we had one of the large kilns completely full we had water dripping on the floor from the condensation. I just wasn't sure of the drying times on the fly. I'll try the schedule you mention and see how it works out for me.

Thank you,

Jack

watershed · Post by **watershed** » Wed Apr 23, 2003 12:50 am

My current experiment on IN kiln drying has been an OK success. There is some cracking in the molds, but since I had them at 1500, for 1-2 DAYS, and repeated that process 3 times (for this batch) I guess that's understandable.

If you haven't been following, these are the molds, that I put a box fan over, in the kiln, for something over 24hrs.

Greg

ellen abbott · Post by **ellen abbott** » Wed Apr 23, 2003 9:31 am

We fill our molds wet. Or mostly wet. He usually makes them one day and I fill them the next but sometimes I fill them the same day. Plus they absorb plenty of moisture during the filling process (which can take up to 12 hours for some of the more complex large bowls) from the gum arabic solution and the water I spritz on the frit to keep it moist. Partner does the firing so I can't tell you anything about drying in the kiln. We rarely get cracks now.

ellen

Nikki ONeill · Post by **Nikki ONeill** » Wed Apr 23, 2003 10:48 am

Ellen: After filling a larger bowl mold with powder and frit is it advisable to let it dry again or can it be fired right away?
Hope you and Mark are coming to WGW.
Nikki

ellen abbott · Post by **ellen abbott** » Wed Apr 23, 2003 11:11 am

It goes right into the kiln mostly. Depends on the time of day of course. If I'm finishing up around midnight, he waits til the next day to put it in. But his firing schedule does allow for cooking out the water at different points. I can't give you the details on this (even tho I've heard his little recital about it many times during demos).

I don't know if we will come or not to WGW. Depends on our workload and our financial situation (we are just now getting to work for the year...spent the first 3 1/2 months rebuilding our shop thanks to termites). Is it still going to be in the NE even tho Bullseye is on board now? Either location is a far piece for us to travel, tho we will be in the Seattle area in Sept (I think) as my niece is getting married then.

I would like to come and meet everybody.

ellen

Nikki ONeill · Post by **Nikki ONeill** » Wed Apr 23, 2003 11:21 am

Ellen: Brad announced that the WGW will be in Arlington Va, (just outside of DC) Sept 11-14. As I understand it, Bullseye will be a sponsor of the event, But the Bullseye glass competition will still be at in Portland. If you do get a chance to come out, there's lots to do here and I know many of the casters and pate-de-verre enthusiasts would like to meet you and Mark. Glad you're now termite free!
Nikki in sunny MD

Jerry · Post by **Jerry** » Sat Apr 26, 2003 8:45 am

And just for the record, I can't wait to meet some of you folks. I'm in Maine, and while Portland is only a three hour drive, it's the wrong Portland for Bullseye.

Mold drying is a matter of preference and nerves. I do a lot of "wet" firing as well but have a fairly conservative firing schedule. Henry Halem's book talks about this and his process seems to work. Basically, heat slowly, 100 dph to 250 and hold for a time to allow the moisture in the mold to boil off. How long is a function of the size of the mold. For one of my smaller castings, about 6" square, I plan a twelve hour hold but watch it and usually go to the next step after about 8 hours. By watching I mean holding a mirror over the top peep hole and looking for condensation. Over several hours there isn't as much coming out and that's when I move on.

The next step is to go to 350 to get rid of the chemically bound water and I usually hold there for a much shorter time; in my small castings it's about 2 hours. The next step is where you can get into trouble because the plaster/silica mix is in the curing process. I go at about 250 dph to 1400 and hold there for an hour to guarantee stabalization. By then the plaster is cured. Then it's up to process and anneal.

I'd like critique on my numbers. I live in the back of beyond and there aren't too many casters out this way so I appreciate advice.

Jerry