I want to make a ceramic copy of an old plaster paris sculpture

I created a plaster of paris bust many years ago. I am now into making molds for ceramic reproduction. I want to make a mold of this plaster bust but do not know what product I should use to make a rubber impression that can later be used to make a plaster mold.

Can anyone tell me what steps I need to take and what products to use for this purpose?

Hi Nikki, I think you should use as basis for the rubber mold latex since that seems to be the most versatile

Hey Nikki,
An old posting but I'll address a few terminology issues. If I'm understanding your situation correctly you have a plaster original and want to make ceramic reproductions of it at a later date?
If you make a rubber negative of the plaster positive (the original) you would then also have to make a rubber positive before you can cast plaster casting molds. (negatives in other words)

For economy sake I would just make a plaster negative off your plaster original. You can then use this plaster negative to cast several ceramic pieces.

I use Murphy's Oil Soap as a seperating compound. It works beautifully and leaves the original clean. (after its dried a few weeks.)
good luck

Thanks Jeff,

I have tried so many techniques using other plaster models. I tried saturating the model with vaselene. Left gaps and was horrible to clean up. I tried using a separator purchased at an art store. Then I used a paint on rubber that covered the model, making certain that I had placed the cutting lines so that I could place the rubber coated half into plaster up to the division line. This worked OK until I tried making the other half.
I was able to slice the rubber at the division line but the original plaster model would not release from the rubber and the completed half of the rubber copy was torn. The first half of the model (the negative of the original plaster model "face"I will be able to use. The second half (the negative "back face" of plaster model) will need to be recoated with rubber and placed in plaster. I created one 5 sided box that I clamped together until the plaster set completely. I have a perfect "face" of my original model yet I have not done the "back face". Once I make both negatives, I will need to create another positve model and I do not know what I can make it of. silicon resin? Or can I just coat each plaster cast of the negative with some releasing agent, bind the two halfs together (being sure to create a "poring" hole, and lock connects?) then pour my slip and time it for the "thickness of the shell" I want for firing?

Hope I haven't confused you.

Hey Nikki,
Very confused. But its Friday.
Do you have pictures?
Perhaps the moderator can link us so you can send direct?

I've used all types of seperators. Smooth-On makes a nice one but I still prefer Murphy's. Most old plaster objects tend to be made of a casting plaster, as opposed to a pottery plaster, and are much harder as a result. In that case I usually apply three or four coats. (lather, wipe, let dry 5 minutes, repeat two/three times)
If I'm unsure I will "seal" with vaseline but I find it doesn't coat the surface as well as Murphy's.

Mold making is a tough biz. Sometimes miracles happen, sometimes not. Years ago I cast a deathmask of a two year old. I had no experience with alginate so I went with plaster. Much to my surprise it turned out beautifully. Miracles can happen.

Jeff,
If you go to the "Photo Album" then to "older photos" there are several photos of my "Hindu Goddess" that I am trying to reproduce as a "poured" ceramic cast. The carvings are very intricate and difficult to reproduce if the coating I use is too thick. Vaseline was out of the question and it took weeks to clean the model. That is why I have experimented with small plaster of paris models before I subject the original to my reproduction efforts.

WOW!
Did you create that? Thats amazing!

On first blush I suspect it will be very difficult to cast in clay (ceramic). Looks like there will need to be multiple parts.
An alternative is to cast it in pieces and then assemble them. (make a mold of each piece, in other words)
The surface textures will complicate the molding/casting process. (as you probably know)
I saw a comment about plaster mixing. Do you have access to a scale? All plasters do have formulas for mixing. Its a pain but it really minimizes poor mixes.

My most parted mold, I've made, was made up of 10 parts. The artist was adament that I not alter the piece. I knew he was a fool but I went ahead anyway. After using the mold one time, and spending $800 dollars, he decided to call it quits. I suggested we cast the piece in several parts, have several molds in other words, but he was certain one mold was best.It took me 5 minutes to reassemble the mold after pouring and I was the guy who made it. If we had broken it down into two or three three part molds it would have been much easier to cast.

Did you make the piece in school? Do you have a studio?

I did not go to school for art, my ability is God given and I am most grateful. It took several samples to get the plaster mix that allowed me to carve the bust. It had to "cure" for months before I could sculpt it into a figure. Had I known it would turn out so well, I would have tried clay or even wood (which I have never tried). Now, years later, I have set up a studio for my painting and ceramics and have decided to reproduce this in a mold. I succeeded in making one half of the head by using your idea of soaping it and letting it dry completely. I then applied a separator, poured the wooden "cast-box" half full of plaster of paris. I had placed "pegs" in the bottom of the box before I poured the plaster of paris. I then set my original into the plaster up to the division line of the plaster. I had already coated the original with the separator and then the rubber was brushed on no more than an 1/8". After two days I broke the box sides away from the plaster. I had already separated the top half of the rubber useing an exacto blade.
I was able to pull the full original model from the plaster mold. It was not easy. May be a good reason to cast in parts. This is only about 16" high by 9" square. the "cast" box I made was 18" long by 5" deep and 6" wide allowing half the "master" to sit until the plaster set. As I said earlier, the rubber mold did not separate completely and can not be used to create another mold. Now, all I have to do is repeat the process for the back side of the "master" bust.

When I have both the front and back molds, I will then be able to pour "slip" to fill it completely. After it sits about 45 minutes or a little longer to make its shell thicker, I will pour out the "slip" (or ceramic liquid clay), and the "shell" will be left inside the mold for another hour or more. Once the "shell" has set it will be considered "greenware". This is where the problem comes in. If the "shell" is too thick, it will explode in the kiln. If it is too thin, it is too fragile to fire. I have fired large vases and lamp bases. I am hoping I can reproduce this the first try. My biggest problem has been in separating the original from the casting mold. I would love to try recreating it in resin after I manage to complete the mold.

Thanks for the compliment.

Nikki,

That sounds really interesting.

Two things, (and I'm a slip casting potter as well), you mention trouble in the casting process, in years past I've added nylon fiber to the slip to increase its strength. You can also add hemp fiber. It thickens it, and makes it more challenging to cast, but with your larger form it just might give you the extra strength it sounds like you need. (at the extreme end it can affect the smoothness of the surface)
Sometimes I leave the clay in the mold overnight. I prefer to pull the clay piece out after an hour or two, but if the mold is particularly wet, or complex, I find the overnight rest much easier to seperate.

Good luck!

People come to me thinking using molds, and the casting process, is really simple. Your description makes it clear that it is not. Especially with comlex forms. Making the mold is one thing, making the clay form, from the mold, is quite another.

Whenever you cast plaster to plaster the old plaster has to be soaked in water until it is about 1/2 wet to 3/4 wet (not totally saturated with water or your soap separator won't dry) Practice with some scrap plaster first so you know when it is too dry or too wet. After wetting your old original apply tincture of green soap(3 parts water to 1 part tincture of green soap available from pharmacies - best are supermarket pharmacies)You want to lather the soap and remove the lather and discard it and apply many layers until you can see a waxy sheen (the soap combines with the surface of the plaster to form a wax barrier) You cannot leave this overnight or the barrier will fail you want to wait 1/2 an hour until the barrier is totally dry and then cast your new plaster against the first half of the model (You want to be sure that the entire model was soaped prior to building your clay bed horizontally in case of leakage of the new plaster this will protect your model from bondage) Hope this helps