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Discussion Starter #1
This is for Buggybuilder from a question he asked me in the pneumatics forum. This is something I put together a year or so ago and I have not checked all the links in this document to make sure they are still active. If you have more questions feel free to ask.

1. You need a some type of skull to start with like DeadSpider shows at this link
http://smg.photobucket.com/albums/v.../Halloween 2005/Prop Prep n Stuff/Misc Stuff/
I used a Bucky 2 piece skull to make molds of it worked great. I have also used the Large Plastic Skull Candle molds for both plaster and foam. The foam has to have a "mold release" I bought some in a spray can from a vendor.

2. Based on the pics the skull is covered with either RTV Rubber or clear silicone. The RTV rubber is normally a shore 30 strength. If you look at the pics the mold is being removed from the foam by turning it inside out. Here is a link to another person that made his own with RTV rubber.
http://www.halloweencreations.com/skull molds.htm

Here is another thread about silicone molds
http://users.lmi.net/~drewid/silicone_faq.html

Here is yet another link on making the molds
http://www.themonsterlab.com/skullmolding1.html

3. This is the method I use since it is much cheaper than RTV rubber

Method on using 100% silicone caulk for making the mold.
http://forums2.gardenweb.com/forums/load/hypertufa/msg1217385422593.html

4. You need to get some clay that is non hardening from the craft store I used plastica clay from Hobby Lobby so you can fill in the eye sockets and nose a little. This is used to cut down on how deep the undercuts are on the mold. The undercuts are the areas that are the most difficult to get the mold removed from the cast and the less the better.

5. Once you have the skull covered with the silicone or RTV 1/2" thick is a great thickness to get it to in layers allowing to to dry in between applications. You need to make a support shell to cover it so that when the foam expands the skull keeps its shape. It looks like DeadSpider used Plaster of Paris and some layers of cheese cloth to make it. Its made in 2 halves so its easier to remove. trust me on that one !

5. The Foam is your basic 2 part Foam A & B the Marine type is a 2LB foam
and it expands the most and is the cheapest and works fine for this application I have also used great stuff spray a little spritz it with a water and spray some more. Moisture is what sets "cures" GreatStuff Foam not Air. The results vary at each cast.

6. Mold release ? Silicone does not stick to much of anything except itself so no mold release is needed. If you have a plastic skull mold like a candle mold the Mold Release from Smoothon is a must. or else the mold is ruined by the foam forever.

I have got bit by the molding casting bug and enjoy learning new things. The Silicone molds work great even for making skulls with Plaster if you want to. I recently melted a bunch of hot glue sticks in a sauce pan and poured it into my mold and make a translucent skull it was kind of neat.

Now is it cheaper ? Well foam skulls are out there in quantity for $ 5 - $8 each and this method will come out close to the same cost when its all said and done with the cost of the 2 part foam but your mileage may vary. But you made them and its fun so why not ?

enjoy :D
 

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Excellent write-up. Thanks for sharing......I have a few questions for you, can you use any type of glycerin to mix with the Silicone or is it specific......also, the reason to dilute the silicone is so that it is thinner to pick up more details and to minimize trapped air bubbles? Im still a little confused on the entire process but Im starting to understand bits and pieces of it........thanks again.:D
 

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Discussion Starter #3
1. Can you use any type of glycerin to mix with the Silicone or is it specific.

A: Not that I am aware of. I picked up a small bottle from Eckerd Drug Store and you don't use a lot. I understood it was to help the curing process of the silicone. It gets the moisture within the silicone. Make the layers sort of thin each time. If they are too think you end up with pockets of "goo" that gets trapped and never cures but its squishy.

2. The reason to dilute the silicone is so that it is thinner to pick up more details and its a little easier to work with and to minimize trapped air bubbles?
Working in a cold environment seems to slow down the process and give you a little more time as well. I did some molds in the winter and then when I did them in the summer it started to skin over much quicker than in the winter.

A: Yes and its a little easier to work with the trade off is the strength so just do it for the first layer to pickup detail or just use a little on each layer to help cure it well. I used a small paper cup each time to mix a batch apply with a small paint brush and Popsicle stick. The paint brush smooths it out. I normally stuck the paint brush in acetone to clean it and threw it out when the mold was completed. Harbor Freight has a good deal on them.

3. I'm still a little confused on the entire process but I'm starting to understand bits and pieces of it.

Yes we all are at least I am learning more each time I create something and read more books etc. The store bought silicone is smelly due to the process it cures but its the least $$$ product and it works for our purposes which we don't care if it messes up here or there that adds "Scare Factor" and you don't want everything looking "perfect" in the first place. Its old its dead it been there a long long long time etc.

Let us see what you make and how it turns out so others can learn and see that its not that difficult to pull off. Smoothon and other companies have some great products to mold and cast stuff with once you get a handle on it.

Here are links that have great stuff:
http://www.smooth-on.com/default.htm
http://www.fxsupply.com/

Zombie-F sorry I cannot seem to figure out where to start my posts and you had to move it. How about a molding / casting section it seems a popular subject.
 

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So you don't necessarily need to use the glycerin as long as you use thin layers? What thickness did you build your mold up to before you casted with it?
Sorry for all the questions, just really wanting to try this soon and Im trying to get a handle on all the supplies I might need. Thanks again for all of your help....:D

.....one other thought I had, since fog juice is glycerin and water, could one use this as a substitute for the pure glycerin?
 

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Discussion Starter #5
So you don't necessarily need to use the glycerin as long as you use thin layers?
Yes it will work without the glycering

What thickness did you build your mold up to before you casted with it?

I would guess to be at least 1/4" maybe 1/2"

.....one other thought I had, since fog juice is glycerin and water, could one use this as a substitute for the pure glycerin?

I have no idea :(
 

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Do you have any pics of your mold? Im stuck trying to decide to use a Block of POP or to make bandages with the cheesecloth.....any suggestions? Also when I apply the first layer of Silicone, since the skull will have a thin layer of petroleum jelly, will the silicone run off of it from gravity or be difficult to get it to stick to vertical surfaces? I'm planning on going for it on Wednesday this week and want as much info as I can get to have a successful first go at it......thanks for all your help.
 

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If you are using 100% silicone from the hardware store, do you need a release agent on your model before you apply the caulk, if so what is the best to use? It will be applied to either a plastic skull or a foam skull as the model....thanks.
 

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Discussion Starter #9
If you are using 100% silicone from the hardware store, do you need a release agent on your model before you apply the caulk, if so what is the best to use? It will be applied to either a plastic skull or a foam skull as the model....thanks.
No release agent needed with Silicone it does not "stick" to much of anything. Just start laying it on. I have to look and see if I have any pictures.
 

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Ok Ive got my skull filled with clay to reduce the undercuts......Ive got my silicone, clycerin and acrylic paint, do I just mix as instructed on the site and start painting the mixture on? Sounds to easy. Did you guys make a box or some way to make the mold in 2 parts? :D
 

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Discussion Starter #11
If you want to make a 2 piece then go side to side and the middle would go down the nose. But a 1 piece can be done just start laying on the layers and the thicker the mold ends up the less chance it will tear. yes its really that simple. Deadspider made a 1 piece using a commercial product that has a very high tear strength. I placed my skull on a square of plexi glass that made removing it easier. Let us know how it goes and take pics
 

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I would love to see pics of your mold. All the molds Ive seen are 2 piece except for that one piece Deadspider has made. Is yours 1 piece or 2?
 

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Discussion Starter #13
I made a 1 piece after my 2 piece failed. I don't have any pics that I took of it that I can find anyway. Just make at least a 2 inch or 3 border around the bottom of the mold and make sure you really thicken up the edges because this is where the stress comes when you pull it. Also the eye sockets and nose get stressed.
 

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I'm sorry to be joining into this discussion so late, but I'm only just now finding the time to join in. lol Mold making is my favorite aspect of the hobby. All but a few of my molds are made from latex. I find it the most economical, and easiest mold making substance to use.
I find that silicon is a bit too flimsy without a mother mold, and it tears much easier than latex does, it also costs more. It also stinks out your house, heehee (sorry Black Cat). On the positive side, it does last longer than a latex mold.
I've heard that dragon skin is wonderful to work with, but unless things have changed, it's way too costly.
I don't think you'll find any difference at all in the amount of detail picked up by any of the mold making mediums though. I use my latex molds to cast plaster, 2 part foam, resins, and hopefully soon wax. I would never recommend using great stuff.

Here are my mold making How tos.
http://terroronbeechwood.com/index.php?pr=Easy_Skull_Mold
http://terroronbeechwood.com/index.php?pr=Mache_skulls_from_mold
http://terroronbeechwood.com/index.php?pr=Making_Latex_Molds

But whatever you use to make your molds, or the medium you use to cast them, I'd suggest that everyone give it a try. We'll be running a How to seminar on basic mold making at the NJ area make and take soon if anyone is interested in joining us.
 

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Im curious, whats the point of making a back up shell for a mold like this one:


Why not just pour straight into the mould with out a shell?
 

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Im curious, whats the point of making a back up shell for a mold like this one
The point of using any mother mold, is when you think that in making your casting, the latex/silicon mold isn't strong enough to make the casting(or pull as they're called) without distorting in shape and ruining the piece. The other reason would be if your latex or silicon mold is in 2 or more pieces. In that case, a mother mold is a necessity to hold the pieces of the flexible mold in alignment.

any tips on using 2 part foam in a latex mold?
Dave, I can only say, that the tendency for two part foam to stick to everything, is only surpassed by great stuff, lol. I use automotive liquid wax as a release agent in the mold, and also outside the mold wherever you think that the foam might spill over. I also use it around air escape holes in the mold. These holes are necessary wherever there is a hollow in the mold. Expanding 2 part foam will not force air out of trapped pockets, and will leave cavities in the finished casting.
Also, I use only disposable mixing cups and stirrers. I use water bottles with the tops cut off to pour the 2 parts into for mixing. After the chemicals mix, the bottles can be thrown away. I use disposable plastic knives as my stirring sticks. I use plastic disposable cups to measure out the 2 part chemicals. Finding the right quantity to use for any given casting is a trial and error process. But I find it better to err on the side of too much the first time, or you wind up with an unusable pull. Most disposable cups have manufacturer grooves on them that will enable you to pour the correct amount each time.
 

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I was going over your skull casting page, Vlad, and I noticed your pics of your recent haunt. How did you make that big trashbag type head with the arms?
 
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