Molding and casting by Kayakasaurus

[Doug Watson]

Ok it looks like I'm going to go with the "dragon skin" and try skipping the hardner. Thank you for suggesting the brush on idea . I found a resin on Amazon that seems to be the least expensive. I plan to order two 16oz for a total of 32. This stuff hardens in under 10 mins, could you see that as being a problem? It has good reviews.

Skip the "thickener" not the "hardener". I know that is what you meant but it made me laugh because when I was with the museum we had this new guy who assured our supervisor he knew how to make moulds. Back then we used a GE silicone that came with a tube of catalyst that you added by drops. Well he prepared this mould and poured the first half at the end of the day it was still a gooey mess, he never added the hardener.

The Polytek resin that is the viscosity of water sets up in 5 minutes so unless you are pressure casting you will be all right. I use a 10 minute set up because 5 minutes doesn't give me enough time to fill all my moulds, clamp the lid on my pressure pot and pressurize the pot.

[Kayakasaurus]

Skip the "thickener" not the "hardener". I know that is what you meant but it made me laugh because when I was with the museum we had this new guy who assured our supervisor he knew how to make moulds. Back then we used a GE silicone that came with a tube of catalyst that you added by drops. Well he prepared this mould and poured the first half at the end of the day it was still a gooey mess, he never added the hardener.

The Polytek resin that is the viscosity of water sets up in 5 minutes so unless you are pressure casting you will be all right. I use a 10 minute set up because 5 minutes doesn't give me enough time to fill all my moulds, clamp the lid on my pressure pot and pressurize the pot.

Whoops! Definitely don't want to skip the hardener LOL. I also totally forgot to paste the link to the product I was describing. Here it is: http://www.amazon.com/gp/aw/d/B0058V9KMK/ref=mp_s_a_1_2?qid=1427217352&sr=8-2&keywords=Casting+plastic&dpPl=1&dpID=5197b9xCuKL&ref=plSrch&pi=AC_SY200_QL40

I won't be useing a pot or vacuum but I think I wil try what Reiner said about rubbing the details with resin before pouring. I can't afford a big thing of polytek so I'll probably go with the above link.

[Doug Watson]

Whoops! Definitely don't want to skip the hardener LOL. I also totally forgot to paste the link to the product I was describing. Here it is:
I won't be useing a pot or vacuum but I think I wil try what Reiner said about rubbing the details with resin before pouring. I can't afford a big thing of polytek so I'll probably go with the above link.

I don't know that material but being a 1:1 mix it is probably a urethane plastic and most of them are pretty much the same and if mixed properly are pretty idiot proof. Back at the museum we used to use a Smooth-On casting urethane that worked the same with a 5 to 10 minute flash time. I can't remember the name of it but if you check them out for a 1:1 mix with the flash time you want I am sure you would find it then you could order all your stuff from the same company.
Looking at the Smooth -On plastics web site I would say it was one of the Smooth Cast 300 series. Just pick one with the pot life that will give you the time to do what you need to do. That is what I mean by flash time its when it starts to go off so you don't want to be just closing your mould when that happens. It needs to be poured by that time. I would try a straight pour first like I said most have the viscosity of water so something like your Shunosaurus should cast fairly easily.

[Doug Watson]

I just noticed the Smooth-On tutorial for the Dragon skin says to use Plasti-Paste for the shell or mould jacket. That will work very well but will be very expensive.
As I mentioned before I make plaster jackets for my smaller moulds if I am doing a large mould then I go with light weight plastic. One of the best ways to do a plaster shell is to use plaster impregnated gauze bandage http://suppliescentral.net/plaster_bandages.html since it already comes in a handy width and ready to dip in water and apply. I myself use polyester cheesecloth that I dip in plaster but that is because I already have a big supply of it. Either way works the plaster bandage is just easier. I lay down a layer of plaster first on the rubber and then lay the bandage on that until I get the thickness I want in the 1/4 to 1/2 inch range.

[Kayakasaurus]

Yah I saw that. I figured  that would only be necessary for big moulds like theirs. We have plenty of materials in our shop for doing repairs that dry rock hard; Fix-all, Durham water putty, or even fiberglass w/ polyester resin. But the cloth idea is good, I might add that in.

[Doug Watson]

We need an "Ask Doug Watson" thread.  I have another question;how do the toy companies label the figures belly with such a small embossed font? Are you involved in that process Doug? I really want to find a way to label my models... Even if it has to be engraved.

I still think your best bet is to get those tiny letters I told you about. You could make a stock piece that you could reuse again and again and just add the name for each one.

[Kayakasaurus]

I got silicone(dragon skin 10 fast) mold release, and resin in the mail today! I think I'm all set. I'm going to do a small test with my Iguanodon egg nest.

To Doug Watson: in the photo of your Smilodon, whence you flip it over and remove the clay do you leave the clay that's in the air channels in? Otherwise they would fill up right? If you have anymore tips or next steps that come to mind I'm all ears! I'll post a pic of my airways before I pour when I do the Shuno.

[Doug Watson]

I got silicone(dragon skin 10 fast) mold release, and resin in the mail today! I think I'm all set. I'm going to do a small test with my Iguanodon egg nest.

To Doug Watson: in the photo of your Smilodon, whence you flip it over and remove the clay do you leave the clay that's in the air channels in? Otherwise they would fill up right? If you have anymore tips or next steps that come to mind I'm all ears! I'll post a pic of my airways before I pour when I do the Shuno.

That's right you need the clay in the air vents and sprue but not in the continuous channel for the key. When you pull the clay the clay in the vents etc pretty much always pull out so you end up redoing them. Make sure your seal is good around your model if the liquid rubber is very thin it can find a hole and leak under then you have to get it off the model on the other side. I seal my plasticine with Vinac (polyvinyl acetate bead) dissolved in acetone that helps prevent the rubber sticking to the plasticine which it does even with a separator. If you don't have an acetate supply you can use shellac. When you mix your rubber try not to whip it up that will add air which can cause air bubbles. I don't know if dragon skin pours but if it does you can pour it in a thin stream and that can help break up air bubbles. Good luck.

[Kayakasaurus]

Wow it sticks even with a release? That is why I'm going to test with the Egg nest, I want to work out any problems. Ok I'll see what we have in the shop. Do you spray or brush on shellac? http://www.rustoleum.com/product-catalog/consumer-brands/zinsser/interior-wood-finishes/bulls-eye-shellac

http://m.lowes.com/pd/Zinsser-Shellacs/3098549

I still am going to try brushing on the silicone even though I didn't get the thickener. If it doesn't work I can always pour but either way I'll try that pouring in a thin stream to get it on.

Thank you for all the advice!! I've been in contact with Brandem as well

[Doug Watson]

Wow it sticks even with a release? That is why I'm going to test with the Egg nest, I want to work out any problems. Ok I'll see what we have in the shop. Do you spray or brush on shellac?

It depends on the rubber, urethanes are worse. It won't stick to the point of ruining your mould but you can end up with a thin film of plasticine in the surface. You may not have an issue with that silicone but I always prefer a barrier.
I would use brush on shellac or else you will have to mask off your model.
Testing is best when I use new materials I will often just prepare a small test piece with all the materials I am using just to be sure. One reminder seal or no seal do not use a sulphur based clay or your silicone will be inhibited in it's cure.
What kind of shop do you work in?

[Kayakasaurus]

Ok I don't work in our shop it's just a big garage . Two years ago we were managing two residential apartment buildings and a commercial one and doing all the repairs and build outs. We sold two though and are living in an apartment of the other building. Anyways when you do that sort of stuff you end up with a lot of tools and supplies. So we have a really handy shop with table saws and all that.

[Kayakasaurus]

Well, I did my test and I'm glad I did.
Here are the results:

1: definitely don't need a thickener! This stuff is really goopy.

2: Do you have experience coloring silicone? Parts A&B are both transparent and dying one would help with mixing. The pigments Smooth-on recommend are to expensive.

3: The mold release worked!!

4: I do have a problem with my clay though. For some reason, it left the silicone that was touching it all sticky. I'm using "Jolly King plasteline" because an employee at a sculpting place recommend it for mold making because it's sulfur free. I googled a bit and found lots of people using it successfully while some people also had the same problem. It seems certain clays can work with certain silicones and you just have to try it. This is a bummer because I have a large block of this stuff. Do you know what could have caused this? Is there maybe a way I could buffer it by sealing the clay like you suggested? I wonder if a layer of mod podge would separate the two? I'm guessing the Amaco air dry clay I have has sulfur or I would use that.

Thank you for answering my questions 

[Doug Watson]

Well, I did my test and I'm glad I did.
Here are the results:

1: definitely don't need a thickener! This stuff is really goopy.

2: Do you have experience coloring silicone? Parts A&B are both transparent and dying one would help with mixing. The pigments Smooth-on recommend are to expensive.

3: The mold release worked!!

4: I do have a problem with my clay though. For some reason, it left the silicone that was touching it all sticky. I'm using "Jolly King plasteline" because an employee at a sculpting place recommend it for mold making because it's sulfur free. I googled a bit and found lots of people using it successfully while some people also had the same problem. It seems certain clays can work with certain silicones and you just have to try it. This is a bummer because I have a large block of this stuff. Do you know what could have caused this? Is there maybe a way I could buffer it by sealing the clay like you suggested? I wonder if a layer of mod podge would separate the two? I'm guessing the Amaco air dry clay I have has sulfur or I would use that.

Thank you for answering my questions 

Sorry you are having trouble.

2. No, I have never coloured silicone but considering the problems you are having I would suggest sticking with the Smooth-On colours, adding another brand might result in more incompatibility.

4. Does Smooth-On have an online Help? At this point I would contact them and detail all the products you are using and ask if there is a compatibility problem. It sounds to me like it is being inhibited by either the release agent or the clay. Sealing the clay might work but I would want to eliminate any chance of that problem by eliminating the offensive product altogether. You don't want to go through the trouble of prepping your model and pouring the rubber only to end up with a gooey mess.

Here is the Plasticine I use. I have used it on many different silicones and urethanes and I have never had an issue sealed or unsealed. Unfortunately for you it is a Canadian product so may not be sold in the USA. But you should be able to source it online and order some cross border. It comes in these 1 lb packages and is scored for easy separation.

[Doug Watson]

I just had another thought. If you have trouble finding the Harbutt's clay a lot of mould makers use modelling wax to dam their moulds. I have only done it once for the museum when I was moulding an Inuit snow goggle because it was an artifact and that is what the conservator wanted me to use. I find it is not as fast as clay but it won't inhibit your silicone and you don't need a separator. You may still need a separator on your model however. You should run a test with the rubber on some cured Magic Sculpt some silicones can be used on Magic Sculpt without a mould release. So you could kill all your problems in one shot.

Oops, you will still need a mould release between your mould halves. So you will want to make sure that the mould release isn't what is inhibiting your rubber.

[Kayakasaurus]

Thank you  . I'm pretty sure it's not the mold release because it was only sticky where the silicone touched the plasteline, the acrylic painted nest was long dry. I have some good news to report. After removing the plasteline from the silicone and letting it be for a few hours it is no longer sticky!! The only thing that is sticky is the plasteline from where the silicone was thin and smeared around the edges. So if the plasteline inhibited the mold from curing it was only extremely thin and it fixes itself when you remove the clay. So I may end up useing it and try blocking it with a layer of mod podge. More good news, I used Durham water puty for a mold jacket and it worked! More good news, I cast the nest and it turned out beautifully! And yes I called Smooth-on and left a message and they haven't got back to me. So I'll run another test today and make sure that mold release works in between silicone and try silicone without mold release on the epoxy as well as dying it, I should be able to do that all at once.

Thanks again  I should have this skill completely mastered just about the time when it becomes commercially available to 3D print cheaper than casting.   

[Doug Watson]

Thank you  . I'm pretty sure it's not the mold release because it was only sticky where the silicone touched the plasteline, the acrylic painted nest was long dry. I have some good news to report. After removing the plasteline from the silicone and letting it be for a few hours it is no longer sticky!! The only thing that is sticky is the plasteline from where the silicone was thin and smeared around the edges. So if the plasteline inhibited the mold from curing it was only extremely thin and it fixes itself when you remove the clay. So I may end up useing it and try blocking it with a layer of mod podge. More good news, I used Durham water puty for a mold jacket and it worked! More good news, I cast the nest and it turned out beautifully! And yes I called Smooth-on and left a message and they haven't got back to me. So I'll run another test today and make sure that mold release works in between silicone and try silicone without mold release on the epoxy as well as dying it, I should be able to do that all at once.

Thanks again  I should have this skill completely mastered just about the time when it becomes commercially available to 3D print cheaper than casting.   

It didn't click when you first said you were using Plasteline. My eyes saw plasticine. Jolly King also makes Roma Plastilina that contains sulphur and will inhibit silicone, I have a brick in front of me now and I know from experience how bad it is. I read online that they claim Plasteline is sulphur free but I wonder if there is something else in it that inhibits silicone. Keep your eye out for Harbutt's plasticine if you can get that you know you will be safe. Harbutt's is originally British and Hobbycraft makes it under licence in Canada so maybe someone makes it in the US under licence. If you use the Plasteline and it inhibits the surface you may lose some detail.
That's the problem you are using brands I have never used so basically it will be trial and error. At least your nest turned out so it looks like you are on your way. Good luck.

[Kayakasaurus]

Ok I did a lot of tests and I think I'm going to have to remove jolly King from the picture. I can't find harbutts plasticine online anywhere, to bad. After Googleing more it seems some people have success with plastiline and some don't, but I'm blaming Smooth on  . Here is a guy who has had the same problem, he made the mold barrier and the positive out of a sulfur free oil based clay with bad results. He decided to stick with just casting baked Sculpey, which brings me to my next idea: I think I'll try unbaked sculpey for making the mold. It's sulphur free and won't dry out. Also it's the only thing anyone carries in the whole country!!(almost)! Well I just got a little money so maybe I can pick some sculpey up today. Wait I just remembered I have a tiny bit... Test time again!!

[Doug Watson]

Ok I did a lot of tests and I think I'm going to have to remove jolly King from the picture. I can't find harbutts plasticine online anywhere, to bad. After Googleing more it seems some people have success with plastiline and some don't, but I'm blaming Smooth on  . Here is a guy who has had the same problem, he made the mold barrier and the positive out of a sulfur free oil based clay with bad results. He decided to stick with just casting baked Sculpey, which brings me to my next idea: I think I'll try unbaked sculpey for making the mold. It's sulphur free and won't dry out. Also it's the only thing anyone carries in the whole country!!(almost)! Well I just got a little money so maybe I can pick some sculpey up today. Wait I just remembered I have a tiny bit... Test time again!!

I found it here online, but they are in Canada.
http://www.myrdalorthopedics.com/product/oven-room-miscellaneous-plasticine-92

or you can get it on eBay out of the UK would probably be cheaper than Sculpey. The only thing is I have never tested it with that particular silicone so who knows it may react to it as well so if the Sculpey works go for it.
http://www.ebay.com/itm/500g-One-Colour-Slab-Plasticine-Assortment-/351360573493?pt=LH_DefaultDomain_0&hash=item51ceb8e035

[Doug Watson]

The other thing you can do is start eating a lot of Babybel Cheese and keep the wax

[Kayakasaurus]

The other thing you can do is start eating a lot of Babybel Cheese and keep the wax

That's funny I actually did that a couple years ago  I think I threw it out though cuz it's not really useful. There are things like that though that I end up using