slburns62 Posted February 4, 2020 Report Share Posted February 4, 2020 I have just acquired a lot of molds. They are molds made out of plaster and are used for making ceramics. What I want to do is use these molds to make plaster items then ceramic items. I took one of the little molds and applied three coats of shellac to seal the inside of the mold. I waited for all coats of shellac to dry, about two days later I sprayed the inside of 50/50 Murphy's Oil Soap. I poured my plaster into mold but when I went to open the mold it crumbles and parts stuck in the mold. I know that these molds can be used for plaster if sealed but not sure how to get the items released from the molds. Please help Link to comment Share on other sites More sharing options...
neilestrick Posted February 4, 2020 Report Share Posted February 4, 2020 I don't know enough about plaster to answer your question, I have a question of my own- what do you mean by make plaster items then ceramic items? Once you've sealed the mold with shellac, it will never work for ceramics again. To use the molds with clay, they must be porous. Link to comment Share on other sites More sharing options...
liambesaw Posted February 4, 2020 Report Share Posted February 4, 2020 Did you let the soap dry? When we use green soap as a mold release it has to be dry when we pour plaster or it will distort the plaster and mix in. Link to comment Share on other sites More sharing options...
Stephen Posted February 4, 2020 Report Share Posted February 4, 2020 Been researching a lot about molds lately and making press molds but I guess I am just not clear on how that could work if they are slip molds like the one below. The way they are designed is for slip to be poured into them and then break away from the piece. Pottery plaster I have found is just not that durable and any undercuts might be the cause of sticking and or crumbling. Maybe try a more dense plaster product like maybe ceramical or hydrocal after you really sealed up the mold. If you get it to work how about posting some pics? I think Neal's right that you really can't use any of these sealed molds for slip later though. Link to comment Share on other sites More sharing options...
Stephen Posted February 4, 2020 Report Share Posted February 4, 2020 16 hours ago, liambesaw said: Did you let the soap dry? When we use green soap as a mold release it has to be dry when we pour plaster or it will distort the plaster and mix in. What's green soap? I'm looking for something other than baking spray, WD40 or corn starch for some wood press molds. Thought I might try murphy's but brushing on green soap and letting it dry sounds righteous! Link to comment Share on other sites More sharing options...
liambesaw Posted February 4, 2020 Report Share Posted February 4, 2020 1 minute ago, Stephen said: What's green soap? I'm looking for something other than baking spray, WD40 or corn starch for some wood press molds. Thought I might try murphy's but brushing on green soap and letting it dry sounds righteous! It's called green soap or tincture of green soap. Tattoo supply places have it for some reason, or some pottery supply places have it too. http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=sps_ecat&Product_Code=72380&Category_Code=RMPL Link to comment Share on other sites More sharing options...
Mark C. Posted February 4, 2020 Report Share Posted February 4, 2020 green soap is also sold thru real (older drug stores) not so much the newer big box ones like Rite Aid /Walgreens as well-call first and ask Link to comment Share on other sites More sharing options...
Stephen Posted February 5, 2020 Report Share Posted February 5, 2020 Also on Amazon, ordered a bottle yesterday delivery today. A pint was $8 and a gallon is $22 with free shipping. If it works well will get a gallon next time. Although I am not using it on a model in pouring a mold I am still going to brush it on some oak press molds and let it dry as Liam suggested. I used baking spray last time and while it worked I put too much on and it mixed in with the clay and was just a mess. Corn starch didn't work very well b4 that and WD40 sounds about as messy as the baking spray. Link to comment Share on other sites More sharing options...
slburns62 Posted February 5, 2020 Author Report Share Posted February 5, 2020 5 hours ago, Stephen said: Also on Amazon, ordered a bottle yesterday delivery today. A pint was $8 and a gallon is $22 with free shipping. If it works well will get a gallon next time. Although I am not using it on a model in pouring a mold I am still going to brush it on some oak press molds and let it dry as Liam suggested. I used baking spray last time and while it worked I put too much on and it mixed in with the clay and was just a mess. Corn starch didn't work very well b4 that and WD40 sounds about as messy as the baking spray. On 2/3/2020 at 7:27 PM, neilestrick said: I don't know enough about plaster to answer your question, I have a question of my own- what do you mean by make plaster items then ceramic items? Once you've sealed the mold with shellac, it will never work for ceramics again. To use the molds with clay, they must be porous. I had read that porous poured in a porous mold would not work. That the mold had to be sealed. I don't plan on purchasing a kiln. I think plaster items are easier. Link to comment Share on other sites More sharing options...
slburns62 Posted February 5, 2020 Author Report Share Posted February 5, 2020 On 2/3/2020 at 7:33 PM, liambesaw said: Did you let the soap dry? When we use green soap as a mold release it has to be dry when we pour plaster or it will distort the plaster and mix in. I used Murphy's Oil Soap and yes I'm sure it was dry and maybe it should not have been. Link to comment Share on other sites More sharing options...
Stephen Posted February 5, 2020 Report Share Posted February 5, 2020 41 minutes ago, slburns62 said: I had read that porous poured in a porous mold would not work. That the mold had to be sealed. I don't plan on purchasing a kiln. I think plaster items are easier. Is this something you have seen instructions on or are you experimenting with this? You mentioned ceramic pieces in your original post but then here say ceramic is not planned? I have just never heard or read anywhere of someone taking slip cast molds and pouring plaster in them. Would love to see the info if you could post a link or two. Don't know about easier but it's different. The plaster whatever pieces will be plaster and fragile. Decorating the finished products will need some sealing as well since it will soak up any paint you try to use and then that has to accommodate whatever you are going to decorate with in that it might look different when put on top of sealed plaster and have trouble drying/sticking. Have fun testing, good luck! If you do figure it out I think there are lots of cheap molds out there, I see large batches for cheap post around often. edit: Also I would definitely consider testing with the stronger ceramical or hydrocal (there I think might even be one more level of hardness) because plaster is going to chip easily. Link to comment Share on other sites More sharing options...
Chilly Posted February 7, 2020 Report Share Posted February 7, 2020 I use soft soap when making multi-part plaster moulds. No sealant. Brush on 5 coats of soap (it has the consistency of thick honey) leaving it to dry thoroughly before applying next coat. The stuff - from Potterycrafts, UK - says to mix it before applying 50:50 with water. Plaster then doesn't stick to plaster. Link to comment Share on other sites More sharing options...
slburns62 Posted February 11, 2020 Author Report Share Posted February 11, 2020 On 2/6/2020 at 8:21 PM, Chilly said: I use soft soap when making multi-part plaster moulds. No sealant. Brush on 5 coats of soap (it has the consistency of thick honey) leaving it to dry thoroughly before applying next coat. The stuff - from Potterycrafts, UK - says to mix it before applying 50:50 with water. Plaster then doesn't stick to plaster. I was told that you do the same as you with soft soap but to use Murphy's Oil Soap. I've not tried it yet but I think today's the day. If this doesn't work I'll have to make the drive to purchase the mold release. Link to comment Share on other sites More sharing options...
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