WarmGlass.com

http://community.webshots.com/album/113692083dyVdgZ

The full view doesn't show the colour accurately; the larger View #2 does.

I used plaster/silica investment, cast in a cylinder shape. The model was was cast in wax from a plaster slip cast mold intended for casting clay. It measures about 6" high and 4" wide at the base. I used homemade SYS96 clear frit. The mold cracked on the way down, and created a few seams.

A few questions:

1. I'm not happy with the colour; it has a dull, greyish cast. Is this to be expected with SYS96 clear frit?

2. The largest seams are about 1/8" wide. Are seams this wide considered acceptable, after coldworking, or would you re-cast the object? View #2 shows the largest seam.

3. Before filling the plaster mold with wax, I coated it with 2 layers of separator: 50/50 Murphy's Oil Soap and water. I was able to pull off one side of the 2-part mold pretty easily, but the other side was very difficult to separate from the wax; I had to mangle the mold to get it off. Is there a better separator to use on plaster molds when casting in wax?

Overall, I'm pleased with the result. It's pretty heavy for such a small thing. I just finished modelling a horse's head (9" high x 9" wide) and a female figure (about 11" h x 5" wide) in clay and can't wait to cast them in glass. I would like to cast them in plaster first, so I can re-cast them using wax to see how different glass colours and other colouring materials will look.

Cheers,
Suzan

That's really quite successful for a first cast. Congratulations.

I haven't used System 96 to cast so I can't answer the question on the color change. You might try their casting billets or I can recommend Bullseye 1401 as a casting glass that stays very clear. If you have room in your kiln to put a flower pot over your mold to drip cast the glass from, you will get a clearer casting and won't have to frit your glass so fine, if at all. It's a good idea to just cast some wedges of different color mixes so you can have a reference of how the glass looks thick to thin.

You have to decide whether you like the flashing or not. It will take lots of practice to make molds that don't check at all if you are pouring tall, solid pieces. Some people hate them and cold work them off, and, as a result, often have to design pieces that won't lose particular details in the cold working. Others decide to embrace and enhance the flashing.

I haven't poured many waxes in plaster molds. I usually use rubber or silicone molds. But I haven't had any trouble pulling waxes from plaster when I've done it. Usually the wax contracts a little and pulls away easily. You might try wetting the plaster before you pour in the wax, not so it is soaked, but just damp. Others will know more about this than I.

ch

Susan, Charlie is right about wetting the plaster mold before pouring the wax. I usually soak a dry mold for a few hours in water then bring it out and let the water drip away or sponge it out so there is no standing water in the mold. Always submerge the mold rather than run water onto it. Running water will erode the mold surface. You shouldn't need any other seperator. Get a candy therometer at the grocery store and pour the wax at about 140 - 150 degrees. If you still have problems with 1/2 of the mold not lifting off cleanly then you probably have an undercut on that part of the mold. If so just find it and scrap away the troublesome plaster. You can always restore the texture in the wax.
Good luck, Ted

I am with Ted on this, though I like charlie just fine. Soak the mold completely and then let it drain off. How long to soak is dependent on size, temp, and humidity but a good way to tell is to soak it and then brush away the bubbles (your hand in the water brushing them off) and then recheck after a few minutes. If no more bubbles appear then the plaster has absorbed all the water that it needs and is ready to let drain. you want the surface damp but w/ no standing water. The moisture is your mold release- you know, the old oil and water trick.

If you have a real pesky undercut and the wax is giving you trouble- warm wax is a little flexible; wiggle vigorously! or try the freezer, cold wax shrinks...

Worst case senario waste that wax casting and find the undercut and clean it up. then make a new wax.

Thanks, all, for your suggestions about wetting the plaster. I had also read that applying lacquer to plaster molds works, so I experimented with two identical gnome molds, (which I am quite happy to sacrifice in the name of glass experimentation).

I applied one coat of Minwax Fast Dry Polyurethane to one mold, and soaked the other mold for about 1 hour. The soaked mold wax came out quite easily, while the polyurethaned mold broke when split apart, and I couldn't release the 2nd side of the wax model at all.

Thanks and Cheers,
Suzan