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Plaster Mold Making & Some Ceramics |
Babalu
Tiki Socialite
Joined: Nov 19, 2006
Posts: 2503
From: Lemon Grove
|  Posted: 2008-04-15 6:16 pm Permalink
Hello All,
Both Bowana and myself have had several folks ask us if we could share a little of what we know on how to build plaster molds for slip casting ceramics. We talked about it, and would love to share some pointers. There are a few few other threads on TC that talk about how to build plaster molds, but I guess one more isn't going to hurt anything. I personally have been playing in water based clays for many years now, but I had no hands on experience with plaster mold making until Bowana did a demo over at my house during one of our "Chop" events.
I did take several pictures of the demo that Bowana and I did for this Chop event which should work as good aid in explaining the processes. It may take several days to get all this information posted on this thread, but I think it will be fun for you, if you find this type of topic of interest.
Well, to start off, a good thing to talk about might be what type of materials can one make a plaster mold from? The answer is basically anything...fired ceramic, wood, plastic, found objects...as I said, most anything, and/or a combination of materials. In this demo I choose to do my cast master form out of an oil based clay called "Plasticine, or Plastilina". This type of clay does not need a mold release agent (mold soap) added to the outside of it in order to pull away from the master mold as the oil in the clay won't stick to the plaster. Plus, one can get some really fine detail in the plastilina, and not have to worry about the clay drying out on you like you would with water based clays. Also, as Bowana put it "this is the way the pros do it" :)
For the master sculpt, I used a 2" diameter PVC pipe as a core material and added the oil based clay to it. This had a few advantages for me...1. I did not have to use so much clay...2. It gave me a nice round shape and predetermined height in and armature to add the clay to. Pictured below are some of the tools that I choose to use when sculpting in the plastilina. "Roma" brand plastilina is a fine choice when choosing a brand of clay to sculpt with. Number 2 Roma is a little softer and has been used mostly for sculpting busts. Number 3 Roma was a little harder and my personal favorive to work with. Number 4 Roma is harder yet...some people like this feel. Please see picture below...Bowana, can you show some of those cool tools you use to work in Plasticine? Please correct me Bowana if you notice me missing steps, or anything elase as we move forward.
[ This Message was edited by: Babalu 2008-05-04 12:22 ]
[ This Message was edited by: Babalu 2008-05-04 20:43 ]
[ This Message was edited by: Babalu 2008-05-05 20:43 ]
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Robin
Tiki Socialite
Joined: Jul 01, 2007
Posts: 402
From: where the road and the sky collide
| Posted: 2008-04-15 8:04 pm Permalink
Whoa! This is gonna be great! Thanks for doing this Bowana and Babalu!!!!!
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Clarita
Tiki Socialite
Joined: Sep 26, 2006
Posts: 1281
From: BA Arg
| Posted: 2008-04-17 06:55 am Permalink
Oh! great thread Babalu, I'm going to stay tuned for sure! Thanks!
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frostiki
Tiki Socialite
Joined: Aug 14, 2006
Posts: 434
From: Mobile, AL
| Posted: 2008-04-17 08:41 am Permalink
Thanks guys this is a great thread, I've picked up a few boos on mold making and none of them compare to what you have posted right here. SImple to understand for simpletons like me. We've been wanting to try our hand at slip casting and this is a push in the right direction.
Mahalo, Frostiki
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Babalu
Tiki Socialite
Joined: Nov 19, 2006
Posts: 2503
From: Lemon Grove
| Posted: 2008-04-17 3:30 pm Permalink
Ok gang, here we go...These were the finished oil based clay sculptures that we started with (the masters). When you sculpt your design you want to make sure you have designed in no undercuts on the master as your plaster molds will need to pull away from the slip formed clay inside the mold when is broken apart. If you have undercuts in the design, it will rip the the clay where the undercuts are located. The Man of War mug shown here is a 4 part mold for the bottom part, and a 2 part mold for the lid. The Oki Doki mug (also shown) is a 3 part mold. As you are sculpting your master, you want to always work thinking about where you want to make your part line on the mold as you go...note the red line on the Oki Doki mug.
I made these simple wood forms. This design makes it easy to be able to adjust the size of the form, and can be used multiple times, for many molds. You want to coat the inner sides of the wood forms with mold soap, or a wood floor soap which will act as a releasing agent...the dried plaster won't stick to the wood.
Next, we started adding a softer cheaper brand of oil based clay(found this stuff at Arron Brothers) to build up on the inside of the form. This will be the first half of the MOW mug. Note how Bowana put some small strips of wood on the bottom which acted a filler so we didn't have to use so much of the soft oil based clay. The clay was built up to our choosen part line on the master.
Note how clay was added to the base of the master and to the top.
Bowana...anything you can add to these steps?
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greentikipat
Tiki Socialite
Joined: Oct 08, 2006
Posts: 325
From: st. pete fl
| Posted: 2008-04-17 3:47 pm Permalink
awesome, guys! this will be a much visited thread for me. well put and great pics.
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Bowana
Grand Member (6 years) 
Joined: Nov 10, 2006
Posts: 1159
From: La Mesa, CA
| Posted: 2008-04-17 10:42 pm Permalink
Sure, Babalu! Pass the mic!
Here is a small, but important thing to consider when designing a slip cast item. The bottom of most mugs, cups, vases, ect. are generally dished in like in this picture. The raised rim around the edge keeps the piece from rocking when sitting upright.
A separate mold part will need to be made to accommodate the undercut caused by the raised rim.
More on how this is done coming up!
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Babalu
Tiki Socialite
Joined: Nov 19, 2006
Posts: 2503
From: Lemon Grove
| Posted: 2008-04-19 3:22 pm Permalink
Ok Sir Bowana...your up. What type of plaster did we use? I don't have access to the name brand from where I am at right now. Plus I can't remember about how long it takes for the plaster to harden...1 hour?
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Bowana
Grand Member (6 years)
Joined: Nov 10, 2006
Posts: 1159
From: La Mesa, CA
| Posted: 2008-04-20 7:54 pm Permalink
Quote:
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On 2008-04-19 15:22, Babalu wrote:
What type of plaster did we use? I can't remember about how long it takes for the plaster to harden...1 hour?
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We used Puritan Pottery Plaster. It takes 30 minutes to an hour to set up hard enough to make the next piece. Hydrocal is also an excellent type of plaster to use in mold making.
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harro
Tiki Socialite
Joined: Sep 05, 2005
Posts: 681
From: Australia / Argentina
| Posted: 2008-04-24 7:58 pm Permalink
Great thread!
Imagine how many cool mugs will be inspired by the instructions contained here. If only I had all this stuff I'd probably give it a go myself! Who knows, maybe one day.
We are all grateful for you guys taking the time to share this valuable information.
cheers.
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Paipo
Tiki Socialite
Joined: Jun 22, 2006
Posts: 1886
From: Aotearoa / NZ
| Posted: 2008-04-24 8:40 pm Permalink
I know I'll be one of those who'll be putting the knowledge in here to practical use. I have questions already, but I'm gonna hold off until I can relate them to what I'll be making...first off I need to get me some clay toolz.
Cheers B + B!
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Babalu
Tiki Socialite
Joined: Nov 19, 2006
Posts: 2503
From: Lemon Grove
| Posted: 2008-04-25 07:47 am Permalink
Thanks guys. Sorry it has taken me sooo long to get back to this thread...I'm just settling back in from that darn trip.
Anyway, "what tools to use" is a good question and one that many wonder about. There are many Sites to buy tools, just Google "Clay Modeling tools" or the like. I pull some pictures from Dick Blick
http://www.dickblick.com/categories/modelingtools/#rubbertippedshapingtools
in order to talk about the subject here.
It's funny, but at one time or another, I have probably brought all these tools on this Site and I find that there are maybe 1 or two from each grouping that I really use. I think each person is different...they like different tools in their hands. Thank goodness clay tools are fairly cheap. Even though I might have brought a pack of tools and only used a few from that grouping, the few that I might have discovered that I liked are worth the cost of the grouping to me.
This is a basic ceramic tool set...clay 101 if you will. Some good tools here. The wire is a must for cutting into blocks of clay(you can make that too).
These wood tools are standard ceramic tools as well, but I also think they work nicely with the oil based clays too.
These metal tools are designed more for oil based clays. I don't have many of these, but I like them...I want to try some more of these here that I don't have yet.
Loop types tools are good all around for removing. I also like to take these and alter (bend) the shape of these to suit my needs.
These rubber tipped tools are great for all around smoothing...love them. When your working in oil based clays, try using just a little "Mineral Spirits" too. This really helps to smooth as well.
Bottom line, there are a shit load of tools out there...you do not need them all! Some of my favorite tools are tools that I made and not ones that I brought.
A question was asked about using a turn table, or lazy susan...yeah, I like these...I tend to use it all the time for all kinds of applications...not just clay.
Well, that was kind of long winded there...hope it helps. I'm going to let Sir Bowana have some fun too...he is pictorially going take this thread home...Sir Bowana...enter stage right 
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MadDogMike
Grand Member (6 years)
Joined: Mar 30, 2008
Posts: 7084
From: The Anvil of the Sun
| Posted: 2008-04-25 09:17 am Permalink
Guys, thanks for the tips! I am in the process of trying one myself. I've never tried any ceramics before, we'll see what happens. I want my mug to be a miniature of my first carved tiki (on the left), which is somewhat simple and crude.
Instead of clay for my model, I started with a 3x7 inch pillar candle and carved it with loop tools. The wax is soft enough to carve easily but hard enough not to damange by handling. It also leaves the tool marks, I'm hoping it will look like carved wood when I'm done. Seems like plaster shouldn't stick to the wax. I've made the model and the mold box, hope to pour the mold this next week.
Babalu & Bowana, I'm about 100 miles east of you, where is a good place in San Diego to buy ceramic supplies (slip, glazes, etc)?
Thanks!
PS The guy in the hat in the pictures looks like BW, a tiki artist I knew back in the 70's!
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little lost tiki
Tiki Socialite
Joined: Jun 12, 2006
Posts: 7551
From: Orange,CA-right near the Circle!
| Posted: 2008-04-25 10:51 am Permalink
BabsBowanabraniacs!
Thanks for this Public Service !
You've just inspired the whole next wave!
you should do instructional videos!
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Bowana
Grand Member (6 years)
Joined: Nov 10, 2006
Posts: 1159
From: La Mesa, CA
| Posted: 2008-04-27 08:14 am Permalink
First of all, I just want to say that this is my 500th post on TC! Yay!
MadDogMike, and anyone else in the SD area: check out Free Form Ceramics in National City for your ceramics needs http://www.freeformclay.com/ They've got clay, plaster, tools, kilns, glazes, and a plethora of other supplies for the ceramicist.
This mug of Babalu's had some complicated design elements to it that required an extra mold piece to be made. Ideally it's best to have as few mold parts as possible, but sometimes having to make more is unavoidable. This picture shows an oil clay separation wall built along the high points of the mug to divide it in half. Notice the 3 buttresses running tangent to the wall. These help strengthen the wall so that when plaster is poured into it, it won't get blown out.
We didn't get a shot of the plaster being poured, but it's done using the same technique as explained on Babs' earlier post. Here's the finished pour with the wall removed. You can see impressions that will form keys on the 3rd piece when it is poured.
Here orange shellac is being applied to the areas that the next mold part will be poured against. Shellac seals the plaster so that the soap that is to be applied next will not soak into the set plaster and cause the pieces to get stuck together. This step is not absolutely critical. Some moldmakers don't do it, but it doesn't hurt. If you've got shellac on hand, use it!
After the shellac is fully dry (15-30 minutes) brush mold soap onto the plaster surface. Mold soap is a liquid soap used specifically for this purpose. I cut mine with some water and put it in a spray bottle. Spray it on, and spread it around with a paint brush, swirl it and make it froth and bubble. This ensures that it has covered all areas. Let it dry for 20 min or so. You'll know it's ready when the froth has disappeared. Now plaster for the next piece can be poured.
We're almost done now! There's still a few little tricks left that we'll cover when we continue, but for now these are the basics of mold making of this type.
Robin, Clarita, Frosty, Pat, Harro, Paipo, MadDog, LLT, we are expecting to see some cool ceramics from you all in the future!
Bowana
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