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Thread: which clay/ Plaster of paris???

  1. #1
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    which clay/ Plaster of paris???

    I am probably getting ahead of myself but... I was at "Michael's" today and went to the clay section... wow.. there is alot in that little isle... Which clay do you all use for 2 part molds and such? I would assume you wouldnt want the drying out type... so that leaves quite a bit more..... What the story with clay... Also I would assume that plaster of paris is all the same??? Looks like there was just 3m brand at "Michael's".. Any advice would be great!!

  2. #2
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    Plaster of Paris is not all the same. For one thing, some of it sets up faster than others, some of it a lot faster. The prices are not the same either. Michaels is probably expensive.

    Most sculptors in the USA seem to like USG #1 Molding Plaster. A place that sells serious building supplies (not a big-box store) would sell it. A 25 pound bag there would cost about what a tiny box costs at Michaels.

    What kind of clay are you asking about? Oil based clay or water based clay? What are you using it for? A two-part mold made from clay? I am unclear on the concept. I make two-part molds from plaster or from rubber.

    Richard
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  3. #3
    Senior Member Tobho Mott's Avatar
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    Might have meant 2 part patterns rather than molds? I've cast some flat backed plaster patterns using hydrostone (stronger than 'regular' PoP, but not nearly as easy to find) but regular plaster should work fine too if you are careful not to break them. If you did mean patterns... I sometimes use a lighter rammer for the first few layers of sand for this reason.

    Give us a little more detail about what you're trying to do, it'll make it easier for us to figure out what you need.

    Jeff
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    Yea ... I'm sorry.. I am new and dont always explain well what I mean... I am mainly going to be doing lost wax casting... I have seen the process setting up a smooth base of clay.. then push the object to the parting line... talc or spray release.. then add plaster of paris... flip remove clay and do it again.. so yes a two part pattern... I just havent found a good list of which clay and which plaster of paris to use.. Sorry guys.. Thanks for the help..

  5. #5
    Hmmm.. I'm a silicone user, but lets see if we can shed some light on the subject. Lets start with a simple part, say a soda can as everyone knows what that is. You will need to lay the can on it's side and keep it from rolling off the table. This can be done with good old plastilina clay. You will build up the clay around the object to the half way point and level it off. Next I would take some junk 1x4 and make a vertical box around it and seal the corners and the base with some silicone in a tube. NOW, it's time to fill the box with PoP. But first you will need to keep the PoP from sticking to the can, the clay and the walls. Booty butter (vaseline) works great for this. Fill the box to the top, let harden. Flip the whole show over, remove the clay, paint everything with booty butter again including the hardened plaster and fill again with pop. After that dries, you separate the two halves of the PoP molds, remove the wood, remove the can, clean out the booty butter and you now have a 2piece negative mold of said can. With a hole drilled into one of the ends, you will pour the wax into the presoaked PoP molds in water, swish it around and dump out. Repeat filling with wax and dumping out until you build up the wall thickness you want. This will take some practice but you get the idea. Learn what a registration tab or mark is. It's important the mold goes back together lined up. This will aid in that process. This is really hard to explain without photos. Once upon a time, we had a brilliant demo of a horse. The photos are screwed, but the text is there. I kept it simple in my description, visualize what I wrote and you should get the idea. People did impressive molds without fancy silicone and other advanced materials. You too can do it. btw, hit up the wifes wax paper in the kitchen, it will make your life easier. Remember, wax sticks very well to dry PoP. You have to soak the mold in water for 10mins or so before pouring the wax in. Think of Zapins video on making simple slabs of wax with a PoP mold.

    You have the basic idea. I get the big box of PoP at lowes in the paint dept. https://www.lowes.com/pd/DAP-25-lb-C...-Paris/3033244 Use that. You can try just about any plastilina clay from michaels for what you are doing. No air dry, no fimo... no sculpy.. Got it? Look for Van Aiken or chavant. Sulphur clays are a big no no with silicones for the most part. You'll be fine with PoP.

    http://www.alloyavenue.com/vb/showth...t-lots-of-pics DAMN SHAME THIS THREAD IS SCREWED! This one was pretty much priceless for molding difficult stuff. Taught the basic principals perfectly.

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  6. #6
    Senior Member Tobho Mott's Avatar
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    I get it now. Thought you had maybe gotten some terms mixed up, but it seems that was not the case, sorry about that. I've done pretty much what jag describes too, to make plaster core boxes for sand casting parts needing hollow spaces in them - I used Lego and the cheapest plasticene I could find instead of 1X4's and any specific type of clay, but other than that that is how I did it too. Worked great!

    Jeff
    Last edited by Tobho Mott; 08-10-2017 at 08:53 AM. Reason: Had a period where I wanted a space... Fat fingers + phone keyboard.
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  7. #7
    For plaster any cheap non-hardening clay will do. If you get into silicone then you have to be picky because it can react with the silicone causing it to not setup (this is bad cause silicone is expensive!).
    Here's 2 good articles/videos on making a two part mold (I have no affiliation with Tested.com just a member and think they make some good stuff). They show silicone but it doesn't matter same technique works with plaster. Just remember what Jag said...Lube those mold parts up or you'l never get them apart in one piece!

    https://youtu.be/DEVi0mEaJJQ

    http://www.tested.com/art/makers/455...on-moldmaking/

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    I will check out those links... I guess when the time comes I will just buy box-o-clay...Thanks guys for the help..still learning!!!

  9. #9
    there you go man. Now you too can make a light saber dildo out of 100bucks worth of silicone. Instead of silicone, you'll be using PoP. Beware of undercuts and crazy overhangs. Best to start with simple shapes first until you get the hang of it. The process is the same without the expense. Keep your plastilina clay clean and you can reuse it again and again. I use vasaline that's been preheated to almost a liquid. Leave the jar in the sun and apply a thin coat with a chip brush. You can do 4 legged animals, but it's a tricky process that involves a big step between front left leg and back right leg on one half the mold and the opposite for the other. Someone here said once that the art in some pieces is the mold itself. I can believe it. I'm dreading running a silicone mold of the roof on this latest lantern. It's not going to be fun at all.
    Visit me: WWW.HandcraftedLanterns.com
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  10. #10
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    I guess I should post elsewhere on this this... how much can you sell light saber dildos for?? LMAO... I have a whole new side business!! As for the vasoline (damn there is a segue!!! ) .. I read online... 75% patrolium Jelly 25% mineral oil for mold release...

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