Excellent step-by-step explanation of why each part of the process is done the way he does it. Very clear. Safety talk is simple and convincing. Thank you!
Yes! But it's tremendously expensive. You can use Fused Silica. This is silica that's been turned from crystaline to amorphous with high heat, but we'd never be able to afford anything bigger than about a golf ball. The good news is simple PPE, good ventilation, and keeping your work station clean will keep you safe. We just had our mold room checked for parts-per-million silica, and it's so safe we could likely be in there w/o masks. Obviously, we ALWAYS use masks. It's likely that a kid playing in a sand box has more exposure to silica dust than we do.
This is so generous! How would I calculate how much mixture to make on a flat slab that is 12"x10"x1" + the 2" of additional space for investment mixture? Thank you!
I'm not sure I understand the question. Could you please elaborate? Mostly I don't calculate material volume for hand-build molds like this. If I don't have enough with the first layer, I just mix and add another layer immediately. Actually, multi-layer molds can be stronger than single-layer, so I'm OK if I don't guess right the first time.
There are a number of places, I would do a search online for Pottery Plaster and Silica Flour. If you have a landscaping center nearby you might also find these materials there. You can also order pre-mixed mold material from Ransom & Randolph (www.ransom-randolph.com/glass). They sell a 50/50 Plaster/Silica mix that's comparable in price to buying/mixing yourself.
Yes, it's critical that water-based clay is still soft for you to remove it. You can use oil-based clay as well, but it's typically stiffer than the water-based and requires more care removing it. Minimal undercuts are helpful, but you can easily remove any clay that you can reach with a tool. That's actually the advantage of this method: since the clay is soft you don't need to completely avoid undercuts to remove the pattern from the mold.
Hello! Great video! Once the plaster is dry and the clay removed, how long should the mould be left to further dry before use? Does it need any kind of pre firing or heating before slumping / casting into the mould? We have tried a couple of times and both moulds have cracked on the first firing, so any tips on this would be very helpful! Thank you!
What's not discussed here is the firing schedule. Predrying a mold at about 110-180ºF overnight can help a bit, but mostly molds crack for 4 reasons: 1. Not thick enough. 2" wall thickness is ideal for most castings. 2. Uneven mold thickness. As the mold dries it shrinks. You want this to happen evenly. 3. Too fast up to 1000ºF. This is the "curing" stage of the firing process. About the minimum time is 8 hrs for smaller molds. 4. Racing through the "quartz-inversion" phase. We typically program a 2-3 hr. ramp from 1000-1200ºF to ease the mold material through this point. You can find more info on the curing/firing stage of casting here: ua-cam.com/video/BlV_iG1zcZA/v-deo.html Hope this helps!
thank you for this so much! very clear and precise! I've been following your steps and it seems my clay was a bit dry and it is not coming off the mould easily? What methods would you recommend I do? Can I use water to wash over the mould? Thanks
Sorry for the delayed reply. YES! You can absolutely used water to wash clay off the inside of your mold... if you're using water-based clay. For oil-based clay I recommend using a mold release and then compressed air to blow the clay particles off the surface.
what would be a method to make it able to handle a mold being blown into? I'm having a hard time finding any information on making molds you can blow into that aren't metal
If you're trying to do hot blow-molds the mix would be the same-1:1:1 plaster:silica:water. However, you either need to make your mold more robust (at least 2" thick) or back it up with a layer of chicken wire coated in more mold-mix. This will prevent your mold from splitting apart during the blowing process. If you're trying to make a mold that you can use several times then it's just Plaster, and you blow into it while cold. For the hot blow-mold you want to preheat the mold to at least 1050ºF before you blow into it. That will allow the glass to fill all the detail. Good luck!
Also, if you don't belong to Glassies on FB, you should try to get in. Huge community of supportive glass folk that have lots of info. Look up the Labold Method, popularized by James Labold. He has a specific way of layering his molds that works super well. I do a similar method, but make mine a lot thinner and constrain with chicken wire.
No, you would cause off-gassing of the plaster and bubbles in the glass. This type of mold is for kiln-casting, which involves loading cold glass into the mold and then firing both the mold and glass to melting temperatures (roughly 1,500ºF).
Absolutely right, but a poured mold (monolithic or block mold) has several disadvantages: 1. It uses more material, since the mold thickness doesn't follow the profile of the pattern. 2. Because a poured mold is less even all the way around it is prone to crack more as it is fired. 3. Making multiple layers increases the strength of the mold and can help prevent catastrophic mold failure where the glass pours out! 4. You don't need any math for a hand-built mold! LOL. If you pour a mold you need to figure out how much mold material will totally cover your patter. This is way easier. Hope this helps!
Excellent step-by-step explanation of why each part of the process is done the way he does it.
Very clear. Safety talk is simple and convincing. Thank you!
Glad you liked it
Thank you so much for taking the time to answer, greatly appreciated! We'll be doing some more tests, fingers crossed!
Great video. Is there a way to replace the silica with something less aggressive for the lungs? Like alumina for example?
Yes! But it's tremendously expensive. You can use Fused Silica. This is silica that's been turned from crystaline to amorphous with high heat, but we'd never be able to afford anything bigger than about a golf ball. The good news is simple PPE, good ventilation, and keeping your work station clean will keep you safe. We just had our mold room checked for parts-per-million silica, and it's so safe we could likely be in there w/o masks. Obviously, we ALWAYS use masks. It's likely that a kid playing in a sand box has more exposure to silica dust than we do.
This is so generous! How would I calculate how much mixture to make on a flat slab that is 12"x10"x1" + the 2" of additional space for investment mixture? Thank you!
I'm not sure I understand the question. Could you please elaborate? Mostly I don't calculate material volume for hand-build molds like this. If I don't have enough with the first layer, I just mix and add another layer immediately. Actually, multi-layer molds can be stronger than single-layer, so I'm OK if I don't guess right the first time.
hello thanks for sharing amazing video but what is the name of the dry stuff and where can i get it to buy both the silicone and plaster powder
There are a number of places, I would do a search online for Pottery Plaster and Silica Flour. If you have a landscaping center nearby you might also find these materials there. You can also order pre-mixed mold material from Ransom & Randolph (www.ransom-randolph.com/glass). They sell a 50/50 Plaster/Silica mix that's comparable in price to buying/mixing yourself.
So they clay is still wet so it peels out? Would it help if there we no undercuts? What kind of clay. Thanks so much
Yes, it's critical that water-based clay is still soft for you to remove it. You can use oil-based clay as well, but it's typically stiffer than the water-based and requires more care removing it. Minimal undercuts are helpful, but you can easily remove any clay that you can reach with a tool. That's actually the advantage of this method: since the clay is soft you don't need to completely avoid undercuts to remove the pattern from the mold.
Hello! Great video! Once the plaster is dry and the clay removed, how long should the mould be left to further dry before use? Does it need any kind of pre firing or heating before slumping / casting into the mould? We have tried a couple of times and both moulds have cracked on the first firing, so any tips on this would be very helpful! Thank you!
What's not discussed here is the firing schedule. Predrying a mold at about 110-180ºF overnight can help a bit, but mostly molds crack for 4 reasons:
1. Not thick enough. 2" wall thickness is ideal for most castings.
2. Uneven mold thickness. As the mold dries it shrinks. You want this to happen evenly.
3. Too fast up to 1000ºF. This is the "curing" stage of the firing process. About the minimum time is 8 hrs for smaller molds.
4. Racing through the "quartz-inversion" phase. We typically program a 2-3 hr. ramp from 1000-1200ºF to ease the mold material through this point.
You can find more info on the curing/firing stage of casting here: ua-cam.com/video/BlV_iG1zcZA/v-deo.html
Hope this helps!
thank you for this so much! very clear and precise! I've been following your steps and it seems my clay was a bit dry and it is not coming off the mould easily? What methods would you recommend I do? Can I use water to wash over the mould? Thanks
Sorry for the delayed reply. YES! You can absolutely used water to wash clay off the inside of your mold... if you're using water-based clay. For oil-based clay I recommend using a mold release and then compressed air to blow the clay particles off the surface.
what would be a method to make it able to handle a mold being blown into? I'm having a hard time finding any information on making molds you can blow into that aren't metal
If you're trying to do hot blow-molds the mix would be the same-1:1:1 plaster:silica:water. However, you either need to make your mold more robust (at least 2" thick) or back it up with a layer of chicken wire coated in more mold-mix. This will prevent your mold from splitting apart during the blowing process. If you're trying to make a mold that you can use several times then it's just Plaster, and you blow into it while cold. For the hot blow-mold you want to preheat the mold to at least 1050ºF before you blow into it. That will allow the glass to fill all the detail. Good luck!
@@kentstateglass5011 thank you so much! I’ve made a couple that have already failed already and I will follow this to a T. I think it will work 😊
Also, if you don't belong to Glassies on FB, you should try to get in. Huge community of supportive glass folk that have lots of info. Look up the Labold Method, popularized by James Labold. He has a specific way of layering his molds that works super well. I do a similar method, but make mine a lot thinner and constrain with chicken wire.
how long doe is take for the mold to set? i made mine outside in the cold and it never got hot, im wondering why?
and if the mold never heated up and still feels cold to the touch a couple hours later if this meand the mold will be subject to cracking in the kiln?
Can you pour molten glass into a mold like this?
Does the mold need to be fired before casting?
This should also work with lost wax casting?
No, you would cause off-gassing of the plaster and bubbles in the glass. This type of mold is for kiln-casting, which involves loading cold glass into the mold and then firing both the mold and glass to melting temperatures (roughly 1,500ºF).
You could have put it in a container and put the sculpture in upside down
Absolutely right, but a poured mold (monolithic or block mold) has several disadvantages:
1. It uses more material, since the mold thickness doesn't follow the profile of the pattern.
2. Because a poured mold is less even all the way around it is prone to crack more as it is fired.
3. Making multiple layers increases the strength of the mold and can help prevent catastrophic mold failure where the glass pours out!
4. You don't need any math for a hand-built mold! LOL. If you pour a mold you need to figure out how much mold material will totally cover your patter. This is way easier.
Hope this helps!
I can understand about half of what you're saying through that mask...
I know! Enable Close Captions, they work surprisingly well!