what do i seal a plaster original with before making a mold?

some say to use an acrylic crystsl clear varnish? and i probably still need to use a release on top of that?

What are you going to make the mold out of? I'd recommend some kind of rubber, like silicone.
I'd seal it with a matte acrylic spray, (if you want it shiny, use the non-matte) and definitely use a good release agent. I like Pam, the cooking spray. Or go to Douglass and Sturgess (dot com) and take a look at their chart of release agents and materials.

Good luck!

if the plaster is 100 percent dry, i would use first a thin coat of shellac,( french polish, followed by thicker coats. shellac drys very fast and is easy to apply,a mould release like liquid vasiline works well, sometimes directly on the plaster.

Welcome to the forum, smackdown and thenoop I hope you both like it here.

That's great info - I hope ablusive will read this soon

I have tried these ideas but you cannot save the original without some damage. Coating the original plaster sculpture with varnish destroys the white chalk appearance of the original. Liquid vaseline will remain in the intricate carved details and it is very difficult to clean if you wish to keep the original.

you need to determine what material you are going to make the mold out of first & whether or not you want a permantly sealed surface.
If permanence if ok - shellac is good for urethane rubber; Krylon Crystal Clear Acrylic Spray is good for silicones (tin & platinum).

Paste wax (Johnsons) is suitable as a sealer for urethanes; petroleum jelly is suitable for silicones...

I HAVE A PLASTER "ORIGINAL" BUST OF A HINDU GODDESS. I WANT TO PRODUCE A PLASTER MOLD OF THE ORIGINAL SO THAT I CAN POUR "SLIP" AND CREATE A "CERAMIC" DUPLICATE OF THE ORIGINAL PLASTER BUST. I HAVE TRIED VASELINE THEN SHELLAC OVER IT THEN CREATED MY "HALF" BOX AND SET HALF THE BUST INTO THE "HALF" BOX AND POURED IN THE LIQUID PLASTER. I HAD TO DISTROY THE NEW "HALF" CAST TO SAVE THE ORIGINAL. I BELIEVE THAT THERE IS A RUBBER COATING THAT CAN BE BRUSHED OVER THE ORIGINAL AND WHEN PULLED FROM THE ORIGINAL (BEING SURE TO SLICE A SEAM TO SEPARATE THE RUBBER IMPRESSION) THEN THE RUBBER COPY CAN BE USED TO MAKE ANOTHER COPY OF THE ORIGINAL BUST. I THINK I WOULD NEED TO CREATE THE COPY IN ANOTHER MEDIUM OTHER THAN PLASTER OF PARIS. IT WOULD HAVE TO BE SOME MEDIUM THAT COULD BE USED FOR A PLASTER OF PARIS MOLD WITHOUT STICKING TO THE PLASTER AFTER IT IS SET. THIS IS WHERE I NEED SOME INPUT. ANYONE OUT THERE EVER DO WHAT I AM TRYING? I REALLY DONT WANT TO LOSE THE ORIGINAL. IT HAS BEEN DIFFICULT CLEANING THE INTRICATE CRAVINGS AFTER MY FIRST ATTEMPT OF COPYING IT.

hi nikki, you need to follow the standard mold making process any foundry would use to take a mold from an original, firstly you must decide if the item can be made in one piece, or it involves a several part mold, lets begin with a one piece, lay the original on a flat surface, then add plastcine or similar around the circumferance to about 5 cms, support the under side at intervales to support the plaster ect, when you have this you can mix and lay on your silicon, apply as many coats as you want, build up an overall thickness of about 1 cm, when this is dry ( a few hours) you begin to flick on your plaster of paris, coat after coat, layered in between with hessian tape to reinforce the mold, when you have a nice thick even covering, and when it is dry, (2 days), you turn the whole thing over and gently prise the plaster away, this leaves you with the original covered in silicon, which should easily pull away, this is then relaced into the new plaster mold which holds the perfect shape, to this you can por cement, plaster, resin, almost anything , to copy your original. some tips, add a good release agent to the original, if it has lots of undercuts, be sure to well fill them with silicon creating a leval surface, you can also add some half round tags to the silicon in order to assure that it fits exactly into its plaster. this will require some question from you, please ask all you need to.

I am amazed by your knowledge! I have "uploaded" the photo of my "Hindu Goddess" made of Plaster. I am not familiar with the product Plastcine or where to get it. Can it be used on a plaster of paris sculpture? Without damaging the original? I am aware of the use of silicone but not the name of a releasing agent. I would like to use the first mold to make a solid replica that I can later make a plaster mold for reproducing a ceramic copy by pouring clay slip. The bust is a "one-of-a-kind" and I want to reproduce several copies for various techniques in porcelain. I will attach the image.

Nikki

this is obviously the best place, to get some pro answers. this is the octopus of power.

hello nikki, plastacine is basically what kids use when playing, its non greasy, non toxic, you probably have another commercial name for it, its not pay dough, its the other one thats been around forever, ok thats one. two, you say you have heard of silicon, but i refer to silicon mold rubber that is a two componant compound used by specialists. i can refer you to my supplier but he is in england, (where are you based?)i have looked at your figure, this must be a two part mold. i will explain the basics, and you can come back .imagine when you look at the piece face on your idea is to devide it into two sections,( not physically)a line must run up the neck arund the chin, over the mouth and nose, between the eyes, up the forehead, and straight back over the head,and down to the base of the neck again, now this line is from where you begin to work. prepare you plastacine into 6cm wide and oncm thick strips long enough for you to handle easily. keeping to one side of the line follow it all over the head, sticking it as you go, when this is done use a blunt but fine tool to gently cut the squashed plastacine into a sharp straight line, following your deviding line, the lay the piece down on its side with the fresh cut side facing up, and support it firmly so that it is stable, your silicon can now be mixed and poured on, this first coat will find its way into all the nooks and crannies, build up subsiquent coats untill you have an overall thicknes of about icm. be sure any undercuts are filled and made leval with the silicon rubber, this then can be covered with the plaster in layers as i have explained,dont forget the release agent. when this is hard (three days) lay the piece plaster down, remove the plastacine wall and you will see the edges of the plaste and the silicon, cut the edges of the silicon straight leaving about two cm all around, now you must coat the exposed edges of plaster with liquid wax in order to prevent the new plaster sticking,( which it will) release agent on the silcon parts, the con tinue with the same plaster process. now you should have a big plaster egg, using a course file clean around untill you can see the join between the twoo plaster edges, now you must atempt to gently prise the two apart, this done you have your mold made, except that you need a hole where you can pour in the final slip. this you can make on the under side using a plastacine bung when you build your walls.

Thank you for your time and effort in the detail you gave. I will keep and utilize it. I hope Copper will also use this for others with a question about mold casting. I have decided exactly where my dividing line will be. I had hoped that it would be possible to coat the bust with rubber (i.e. silicon) or any other material that could be removed from the bust without sticking to it. I had this idea of using liquid paraffin, allowing it to harden, one side at a time. I just didn't know what material could be poured into the paraffin mold to replicate the bust. I could destroy the paraffin mold but the duplicate bust may present the same problem in creating a plaster mold. If I weren't afraid of making a mistake in the creation of the mold, I would be willing to destroy, if necessary, the original bust. I am in the states but order my art supplies from all over the world. I have made many purchases from the UK.

Thanks again,
Nikki

In order to make a ceramic slip casting mold over a plaster positive you first want to soak the model 1/2 way in water so that it is partially damp (not so damp that the water remains on the surface of the plaster) run some test on plaster pieces so you know what 1/2 way saturated with water is before you do this to you model or you will have to wait for it to partially dry. Tincture of Green Soap is the best separator for plaster positves to plaster negative molds. You have to dilute it 4 part water to 1 part soap and then lather it onto your plaster positive quite a few times till it has a waxy sheen. It has to thoroughly dry for about 1/2 an hour before you pour your first mold 1/2 so by the time that you set up the clay bed it will be dry. I always throw on one more coat to be sure and let that dry 1/2 an dhour and then pour the mold piece. You have to soap the mold boards as well or you will get expansion cracks from the corners of the mold box. Do not leave it overnight or the soap film will crack and fail as a barrier. my e-mail is This e-mail address is being protected from spam bots, you need JavaScript enabled to view it , but I only check e-mail a few times per month.

You also have to plan where you want your seam lines. It is never desirable to put the seam line up the middle of the face because the slip cast pieces if they are unglazed will be slightly discolored on the seem because of the way that the clay particles allign in the plaster negetive mold. You have to plan for undercuts with slip casting and it is difficult to tell from your model if you have any. Go to American books in print or British books in print for good books on making slip casting molds. Plaster Model and Mold Making by Chaney and Skee is a good American book for slip casting molds for beginners. Practice first with something small before you risk your sculpture as it looks very well sculpted. I am somewhat computer challenged and don't know how to upload pictures to this site which I just discovered today, but there are a few slip casting books on the market. The author Frith puts one out but it is $50 US currency and a bit pricy but very good. In America you can go to www.yellowpages.com and connect with old time mold makers in the Trenton, NJ area which used to be where a lot of ceramic hobby molds where made. Laguna Clay in California also will give you free advise and if you go to www.skype.com you should be able to talk to them internationally for free. Your artwork is very nice and you obviously have a lot of talent. Keep up the work and you are welcome to write me any time to my e-mail - just don't expect quick answers as I am looking for a 2nd part time job right now and don't have Internet I use it in the library. When you put the green soap on you have to lather it, remove the lather, and then reapply it a lot of times. It becomes a wax barrier to the new plaster you are casting and it won't transfer to the mold piece and inhibit the slip casting from casting. You can take half water and half vinegar(acetic acid) and sponge out the inside of the plaster mold if you have any problems.

If you are making a plaster mold from a plaster model the plaster model needs to be 1/2 wet befor applying tincture of green soap (3-4parts H20 to 1 part Tincture of green soap) you want to apply the diluted tincture of green soap with a soft brush and lather it all over the model including the bottom incase of leakage. Keep reapplying the tincture of green soap until you build up a waxy surface ( it turns to wax ) You want the plaster model to be 1/2 wet because if it is totally dry then it will steal the water from the newly setting plaster and the barrier could fail. It should be applied about 1/2-1 hour before pouring the plaster.

When ever doing rubber molds you should use the manufacturer recommended separator or run a small test with johnson's paste wax, vaseline, tincture of green soap, silicon spray, eTc.

Sorry I have been too busy to reply to your wonderful and knowledgeable suggestion. It appears that you really understand what I am trying to accomplish. I want to produce a Plaster negative "mold" from a Plaster positive "sculpture".

I do hope you or someone will tell me where I can get tinture of green soap. I have rubber mold and a releasing agent. I also know how to make 1/2 at a time, equally divided. The tinture of green soap did not come up in any of my research.

Thanks again!

I thank everyonewho offered solutions to my question in regard to making a plaster mold from a plaster model with no damage to the original.

After much deliberation and review of suggestions, I am going to attempt the following;

1) I will spray the positive "original" with several coats of shellac.

2) After coating "positive" with a releasing agent and/or tinture of green soap on the first half.I will then brush half the "positive" with silicon rubber to a predetermined "seamline".

3) I will prepare a four sided box, 18'L x 8" W x 8" D, clamped at all four corners. It will have a 2" wooden peg attached to the bottom that will support the "positive" from sitting on the bottom of the box and be used as a "pour hole" when mold is finished.

4) Then I will pour my premixed plaster into this wooden framed box to the depth of the peg.

5) I will place the "positive" into the box and then fill to the "seamline" on the "positive" making certain to leave "key" holes for locking both halfs together when second half is made.

6) After the plaster has dried a few days, I will then remove the sides of the box. I will keep the "positive" in the first half of the cast and soak it in tinture of green soap. Making certain to coat with releasing agent so second half will release from the first half.

I will then repeat the same proceedure for the second half hoping to remove the mold without damage to the original.

I will take photos and post them if this works.

Anyone with a better idea, please feel free to reply.

The model I wish to copy is the "Hindu Goddess Bust" appearing in the "Latest Hot Photos"

Sounds good, Nikki. Wow, very thorough thinking! I don't see any reason why this wouldn't succeed. I look forward to hearing how it worked out and to the photos afterwards

Copper,
Nice to hear from you again. You never replied to the email I sent with the paintings.

Anyway, will be trying out the mold idea soon and let everyone on this site know the outcome. Keeping my fingers crossed that it will not damage the original.

Nikki, I never received an email from you Ohhhh I feel like I really missed something

It's good to see you around here again, Nikki I will also keep my fingers crossed for you (with 4 crossed fingers we should be able to steer luck the way we want it, right? )

I will resend it, complete with pix to the other email address you gave me. Let me know today if you get it as I may not have gotten the right email add. down.

Nikki, you might have a wrong email address of me because I still haven't received it

My email address is This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .

Is that the address you're having of me?

I am very much looking forward to receiving photos of your undoubtedly beautiful work