no adding water, that's nuts, and no need at all for graphite either plaster silica doesnt stick to glass. save the trash in a can for mixing into your next mold to save material and improve ventilation, or you can add talc by 10%. the fired material (called ludo) is reusable for later molds. this can be a wooden box or even metal if needed. for blow molds youll want to make a flask to hold the material in after its fired. the firing should be very slow and low temp for several hours before going over 500º, then up to 1000º for a soak, then just crash the oven, best results are hot blow molds but you can also use cold. The mold will have water in it and that will need to be removed in a kiln. pour and let set up for about two hours before moving. it will "cure" in about ten minutes so be ready to pour it out right away, no tie to fix a mold wall or run and get whatever you forgot. this mixture should then be thouroughly mixed making sure all dry clumps are sufficientlt broken down and the thickness is that of a heavy milkshake. then let sit for about two minutes and dont do anything at all, no touching except for tapping the side of the bucket to release bubbles. start with half a five gallon bucket of water, add until the "island" remains, even after tapping the side of bucket a few times. a scoop of pottery plaster ,a scoop of silica flour #200 mesh. that is the standard ratio, you can tweak later.Īlways add your dry material to your water. Hope that helps.ĥ0/50 plaster silica to 50/50 water and dry mix. I think there's a whole chapter in there about mold blowing. The way I learned mold blowing is from that Advanced Glassblowing Techniques book. I always mixed it just well enough to get the clumps and bubbles out. Basically it's about getting the mix of plaster and water just right. I'd look around on youtube for videos about it because I don't think I could explain my method well through text. It's pretty fickle and I only had success with mixing it after someone showed me how in person. You'd make the mold and soak it in water before you use it and coat the inside of the mold with graphite powder to help the glass release better and have some vent holes will help the glass fill the mold better.Īs for plaster, it doesn't dry so much as it cures. Also plaster is a stronger than silica so an all plaster mold would hold its shape better. Your blow mold doesn't need to do that so plaster should work fine. From what I remember silica is more something you'd use for molds you're using in the kiln because it can withstand high temperatures for a long time. The way I learned to do it was with an all plaster mold. but I can’t seem to find much in the way of plaster+silica mold knowledge as it’s pretty glass blowing specific.Īnyone know of a resource or can you offer any insight? I held onto the original shape I carved in clay, so in theory I could cast the mold again pretty easily. I figured low temp over a long time was best. I’m in a moist environment and I know if the mold isn’t fully dry the water can expand when it’s used and bust the mold. Did I need to mix them longer? Should it be warming up when I pour?ĭoes the silica change what I should expect in the process?Īfter I finished the mold I put the halves in the oven to dry out. When I mixed both sides I mixed them for about 5 minutes. I’m wondering if I didn’t use enough plaster and maybe it didn’t set up properly. I mixed the first batch of plaster and it had some standing water for a bit before it set, and when it did set it didn’t seem as warm as I anticipated when it did it’s thing. I have doubts about the structural integrity of the mold. I didn’t have any undercuts or anything, my mold came apart, and I have two pieces that are most definitely viable form wise. I’m wondering if anyone else has tried it, and if so, I have some doubts that maybe you could clear up. Has anyone used a plaster and silica mold? I’m trying to make a basic mold but don’t have a ton (but some.) experience with plaster.
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