# Lots of skulls from liquid plastic and foam



## havok1919

I wanted to get a lot of skulls this year (like minor The Killing Fields quantities) but I didn't like the look of the commercial plastic 'Halloween' versions and at $15 a pop the 4th quality anatomical ones would be too expensive. (Not to mention heavy-- they're close to 3lbs each!)

Casting my own in liquid urethane plastic and foam seemed like a good solution. This is what I did:

Start with one of the $15 "4th quality" anatomical skulls available online:










I didn't want to have to make a *really* complex multi-part mold, so the shape needed to be a closed surface-- essentially there could be no "loops" in the skull or else removing the silicone molding compound would be impossible. I started off by using Bondo to seal up parts of the skull and build up the volmer to make it more visible. (When making castings it's easier to have something there and carve it away on the 'copies' if need be, than to try to add it.)










The side of the skull presented a problem since you really expect to see that open "hoop" from the zygomatic bone... But it would be impossible to remove a part from the mold if it was cast that way. To work around that I put a piece of Saran wrap on some clay and gently blocked the base of the 'hole':










Here you can see it from the other side:










I used a tube of 60-second epoxy to squirt in a thin layer on top of the cellophane and once it set, removed the clay backing, leaving a thin skin of epoxy as a barrier.










With the prep work done, I started off with a thin ("detail") coat of silicone mold making compound. (I used the Silicone RTV system from Tap Plastics-- about $24 for a 1lb tub, but Smooth-On stuff or whatever else should work. I like Silicone because although it's more expensive than latex or urethane rubber you don't have to worry about the plastic sticking inside it.) The first coat just gets dabbed on with a brush to get in the little nooks and crannies for fine detail:










Additional layers of silicone are built up to give the mold strength (I added a little pigment to make it easier to see what I've coated with each pass):










Finally, after a few thin coats a little thickener is added to the next layers to make the silicone a more paste-like consistency and the mold is built up for more durability:










Where the mold will be cut, a thick ridge is built up to reduce tearing. The plastic will just pour in the hole in the bottom.










With the mold done, I used some Smooth-On "Plasti Paste" to build a support shell. This keeps the silicone mold from distorting during casting. Plasti Paste is about ~$30 for a trial size and I used maybe half of it for this project. I applied the paste in four sections (taking care to apply some mold release where they need to separate).










(splitting here due to limit on number of inline pictures!)


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## havok1919

(and picking up with 'part 2')


When the Plasti Paste cures it's a lighter color and it sandable, drillable, etc. It's pretty tough stuff.










I added some reinforcement 'tabs' and drilled some holes to put carriage bolts through to help keep the shell in place. Since I'm going to fill the mold with an expanding foam that can actually push the mold apart from inside if you don't secure it. If you were only going to cast in plastic and leave the parts hollow you could just use rubber bands.










Once the support shell is done and removed I made a couple cuts in the silicone-- just enough to remove the original skull. I the original can come out, so can the cast copies. Here you see the silicone mold turned essentially inside out. The silicone captures *all* the features of the original-- right down to fingerprints if you left any! 










My casting technique used the basic urethane plastic "Quik Cast" from Tap Plastics. Just so happens it's a 'bone' color. ;-) It's about $26 for the "pint" sized version, but the per oz. price comes down in larger volumes. The plastic mixes 1:1 by volume and I finally arrived at about 70ml of each part for the skull. The plastic is poured in the base and then slushed around to evenly coat all the interior of the mold. Once the plastic starts to set (you can see it start to turn from a cola color to tan) I place the mold teeth-down, so that the excess liquid pools in the teeth to help make those stronger

After about 10-15 minutes (depending on temperature) the plastic will be cured. I then used some of the Tap X-30 expanding foam to fill the interior to make the casting stronger. About 50ml of each part of the foam (~$28 for the quart size) expands to fill the entire skull. Again, I slush the liquid around inside the skull to get it up around the thin bones in the eye sockets for added strength.

The expanding foam takes about ~10 minutes to set up where you can demold it from the shell. I like to remove the casting at this time when it's still *slightly* pliable since it's easier to pull out some of the larger features (like the eye sockets and teeth).










If done right, you get a perfect copy of the original. Since the silicone doesn't need a mold release agent applied, the resulting castings are easier to paint too. Once nice thing about doing 'bones' in this way is that if you *do* have an "oops" and break something off when demolding (or if the plastic didn't go everywhere you wanted it to) it just looks like a normal damaged bone. 










I yielded about ~9 castings from my smaller quantity liquid resin containers which puts the cost at about $2.50/ea. If you buy the larger volume plastics it's more like ~$1.50/ea. The mold will last for years, so although it cost another ~$30-50 depending on how much silicone and plastic you use, you could literally cast 100's if not 1000's of pieces with it. 

It's not a *cheap* process to get started with, but it produces very nice quality output. Depending on temperature you can do about ~3-4 per hour taking your time. Only about ~5 minutes or so per cycle is actually spent 'baby-sitting' the mold, the rest of it is just waiting for the materials to set.

Let me know if you have any questions or need to see more pictures of anything.

-Clay

[Edit: P.S. The resultant cast parts are about ~6oz where the original cast skulls (without jawbone) are about 45oz! Much easier to deal with when putting a lot together as a sculpture/architectural element. 10-19-2010 -- revised per piece pricing based on current Tap Plastics rates.)


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## partsman

Very cool, you can just drop that whole pile of skulls right in the mail to me  Seriously though those came out great, too bad you cant find nice skulls like that in the stores for around $5 a piece. I'd seriously buy some of those for my display. (Hint...Hint)


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## Smiter

You make it look soooooooooooo easyyyyyyyyyy,,, 
Seriously though... GREAT JOB, and thanks for sharing!


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## DannyK

great looking product...I have zero experiance with mold making, but would love to try to do something like this. is there a cheap, quick and dirty way of making a mold for something "halloween useful" that I can hone my skills on without the $100ish investment on high quality silicone and latex stuff? Can I substitute great stuff type foam in my practice molds vice using the expanding foam that you mixed?

thanks for any advice you can lend me.

dK


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## UnOrthodOx

DannyK said:


> great looking product...I have zero experiance with mold making, but would love to try to do something like this. is there a cheap, quick and dirty way of making a mold for something "halloween useful" that I can hone my skills on without the $100ish investment on high quality silicone and latex stuff? Can I substitute great stuff type foam in my practice molds vice using the expanding foam that you mixed?
> 
> thanks for any advice you can lend me.
> 
> dK


I have a latex mold tutorial over here that can be done fore $20 or less. 

http://www.halloweenforum.com/tutorials-step-step/67547-glove-mold-making-101-a.html

Let me be clear, though, you get what you pay for. The silicone mold would last essentially forever. The latex ones, not so much, 2-3 years ish.


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## cyberhaunt

This is awesome, thanks for showing us how. One of these days ill muster up the nerve to give it a try.


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## havok1919

DannyK said:


> is there a cheap, quick and dirty way of making a mold for something "halloween useful" that I can hone my skills on without the $100ish investment on high quality silicone and latex stuff?


You can make molds out of lots of different materials depending what your requirements are for the final product (if you need to perfectly reproduce something vs. just make a neat shape or if you need to cast one vs. one hundred copies).

What I started with way long ago (before I had access to any "better" materials) was just plaster of paris. A simple one to do is just make a little mold box (nothing more that cardboard box lined with plastic, or some old tupper-ware) with a 'U' shape cut in one end. Pour in liquid plaster of paris and coat your hand/wrist/arm with vaseline and submerge it halfway in the plaster (using the 'U' to place your arm in). Hold still and wait until the plaster hardens (the toughest part!). 

Brush on more vaseline on the top of the (already set) plaster and pour in another batch of plaster on top. (Helps to have a second person helping here. ;-) You can add some gauze or other fabric to help the plaster be a little harder to break. 

Once the plaster is set, you can gently pry the two halves apart and pull your hand out and you have a nice mold. Give it another thin coat of vaseline to make it easier to remove the casting.

At that point I'd actually just use a tube of tan latex caulk (usually a few bucks at a hardware store) and smear a thin layer (1/8"?) inside each side of the mold. You don't want too much or it won't cure, but if done right it'll make a nice flexible "skin" casting of your arm that will pull out of the plaster without breaking it. (The cure time can be pretty long on the caulk.) You can then put a few shots of spray foam inside to firm it up or fill it with some styrofoam cut to look like bone, etc. Another thing to experiment with for rubber/flexible like casting is "Plastidip". (Used for coating tool handles, etc.) It's a little more expensive, but probably still under $10.

While not a substitute for the high priced materials in all cases you can still do some neat stuff on a limited budget. Typically you'll have to wait longer for things to cure and have less 'optimal' properties with the final product, but it's worth playing around with.

-Clay


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## GodSpeed

Could you just fill the mold with the X-30 and have a entirely foam Skull?


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## havok1919

GodSpeed said:


> Could you just fill the mold with the X-30 and have a entirely foam Skull?


Yep, that works. Conversely, you can use a little more liquid plastic and leave it hollow and still be plenty strong. Smooth-On makes a version of one of their liquid plastics specifically for rotational casting that would work well too. (It's specifically designed to gel and sticks to the sides of the mold as it sets.)

For this particular skull (supposedly anatomically correct) it takes about 50ml of each part of the X-30 foam to fill it. You'd get about ~35 shots from a 1/2 Gallon set. So that'd be about $1.25/ea if you have a local Tap Plastics (or similar) to pick up the material at and avoid shipping charges. Pretty cheap!

When casting with the foam only you might want to try to make the mold so it's fully sealable (with just a couple little vents for air to escape)-- that way once you dial in the exact amount of material to use you can cap it off and get a denser, closed cell foam to capture the detail. Since I kept the thin bones on the skull anatomically correct I used the plastic 'skin' for strength-- I didn't want to risk breaking a foam-only version but it might be overkill.

-Clay


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## Caitsith

That is some awesome work. You can never have enough skulls! These are some that I'm working on right now. About 20 peices. This isn't everything, just whats currently on the dining room table. (Wife wants her food table back!!!) These are all paper mache' and aluminum foil without the paper. My own extra thick mix. A good example of very cheap... Cait


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## havok1919

Those look great, Cait!

I've been trying to get 3-4 of mine cast each evening as I wander in and out of the shop doing other stuff-- pour plastic one time, pour foam the next, etc. I'm up to about ~13 pcs now. I figure I should be able to get up around ~30 by next weekend-- then I need to do a mass skull painting project!

We have a couple of columns on the front entrance to our house, so my first plan was to connect them with a skull archway over the top, but I think I might start at the bottom and move up-- stacks of skulls sorta spilling out on the floor from each column base. We'll see how it goes. I always start too late! ;-)

-Clay


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## Screaming Demons

Rite-Aid has them on sale right now for $2.49.


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## havok1919

Just a little update for those of you that were curious...

I've dialed the mold in a little better-- I'm using 50ml of each part of liquid plastic and 45ml of each part of the foam. Also, the 32oz containers of the Tap Quik Cast plastic are only $25.50... I should get at least 19 skulls from each-- so ~$1.34/ea in plastic. Not bad!

The 64oz X-30 foam is ~$43 and I'll get at least 42 skulls from that, so only $1.03 there, so that makes for $2.37-ish in materials. I can live with that.

I'm over 20-something now:



















Also, I noticed a potentially useful/interesting effect. If you're impatient (*ahem*) and pull the casting from the mold too soon it remains pretty soft and you can kinda scrunch it up and make interesting distortions in it. Totally accidental discovery, but it's kinda neat:










-Clay


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## billman

Pretty cool!....any shrinkage problems?


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## havok1919

billman said:


> Pretty cool!....any shrinkage problems?


Nope! The plastic is designed specifically for casting and it's very low shrinkage (<1% per the datasheet-- 0.01" per inch). The X-30 foam is also *really* rigid. It seems much 'harder' than something like Great Stuff. The Quik Cast is a fairly brittle plastic when cast in small sections though, not like the TASK plastics from Smooth-On that can deflect quite a bit.

I like the X-30 now that I'm using it more; I don't think that Smooth-On has any foams that expand to 30 times the volume like that, so you use a lot less of it for the same coverage.


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## VexFX

Gotta love silicone! (and tap plastics)


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## TNBrad

Oh this is so cool

thank you for sharing


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## bldaz

Wow, very impressive. You have skills my friend. Love to try it but cant go the 100 bucks right now and we are out of time. The possibilities are endless though. You should seriously sell those.


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## ScreamFX

Those look really fantastic. You wouldn't have a technique to make them hollow, would you? I was thinking rotocasting might be the only way, but I'm sure there are other techniques.


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## Phantom Blue

Thanks havok1919! Been wanted to do this and have been waiting for some extra funds and a good tut. Found the tut now need the $$. Maybe I will find some X-30 in my stocking this years?

PB


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## Samhain1031

Now I have to invest in enough containers to hold all of these bad boys.


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## Phantom Blue

or you could send me your extras...I will put to good use!


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## LT Scare

Caitsith said:


> That is some awesome work. You can never have enough skulls! These are some that I'm working on right now. About 20 peices. This isn't everything, just whats currently on the dining room table. (Wife wants her food table back!!!) These are all paper mache' and aluminum foil without the paper. My own extra thick mix. A good example of very cheap... Cait


Really great job and closer to what I need for my particular application. The Plastic skulls look like great quality. But I need quantity and I need to cut them to hang in our catacombs area.


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## EveningKiss

Love this!. How much did you spend to get started? I may have to try this in a few weeks when i do my pillars =)


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## tupes

These look great. Good job.


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## ManufacturedFear

very good thread, thank you for posting. I'm logging this to come back to later


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## LT Scare

I used sand casting and various plastic skulls for impressions, with Great Stuff foam to make a couple hundred skulls this year. They aren't as realistic looking as the mache skulls, but when sprayed black they look pretty creepy.

I made two of these pillars. This one is three sided (doesn't kill the grass under it). The other houses (weather prooffs) speakers, amp, DVD player and projector for the Disney singing busts.







It had been misting so I bagged the fire pots in this pic (set up was in progress):










This is an early pic of the catacombs. About 75 more sand cast skulls were added to three walls in here:


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## scubaspook

How many coats of silicone do you think you used? I am attempting this poject but it is not turning out well. The silicone justs wants to slide/drip off.


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## scourge

Very cool Havok! You can never have to many skulls! I just wanted to pass on that silicone molds can last years depending on frequency of use and the material being cast. Other factors like how the mold was made can also help prolong the life of the mold but they do wear out. In most cases the silicone mold "stretches" and will begin to fold inside the mother mold before things like resin or foam begin to stick. I blow through molds on a regular basis due to production wear. But that said you do get great bank for your buck here with piles of skulls!!!! Awesome work, thanks for the post and photos!


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## Pennywise

I'm doing this for sure. Can I use just foam instead of the plastic to cast these? I'll definitely be going with an expanding foam (not Great Stuff), so I'll be pricing out the products. Thanks for sharing!


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## LeeAction

this rules


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## LT Scare

Pennywise said:


> I'm doing this for sure. Can I use just foam instead of the plastic to cast these? I'll definitely be going with an expanding foam (not Great Stuff), so I'll be pricing out the products. Thanks for sharing!


I'm unclear about the difference between Great Stuff and expanding foam. I sprayed GS into a sand mold I had just "dusted" with WD40. Spraying it level with the sand resulted in a back half-globe that could be trimed to meet my purposes. I cut the back of the skull at different flat angles to mount them "looking" in all different directions. The finer the sand the more real looking, but my application used black painted skulls with LED eyes in most cases, so rough sand worked great and was quick to reform after each batch dried. FWIW


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## havok1919

Hey Everybody-- I haven't checked in in a while! (We did a commercial haunt in 2012 and that burned me out on Halloween for a bit!)

Misc. comments:

* Yes, you can can directly with foam instead of the first slush-casting with plastic. It won't be as strong (expect thin parts to break when demolding) and the surface won't hold detail quite as well.

* Great Stuff may work if you did thin layers, but I suspect that it would be hard to get it everywhere it needs to get and it probably won't cure very well compared to two-part foams in an enclosed space. (For a 'dish' type mold or the 'face' sort of sand molds GS will cure because half of it is exposed to the air, but putting it in a container like my full shell mold is really about like keeping it in a can-- so it can't fully react and cure solid.)


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## budude

I did a similar mold last month but bolted down to a board for a flat bottom. I'm using Smooth-On Foam-iT 5 (10x) foam with about 4oz of each. I found that the bottom of the mold (top of the skull) appears to get very hot during the expansion and it bubbled up quite a bit. I'm not sure what I'm doing wrong as the rest of the mold turns out pretty good. The end result is still usable but I have to sand down the crown of the skull to get it smooth - just more work/time that I don't want to do... I'm guessing that the board is forcing too much compression or something but if I don't have it, it won't conform to the jaw line and other bits at the bottom of the skull (top of the mold).

Any ideas?


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## havok1919

budude said:


> I found that the bottom of the mold (top of the skull) appears to get very hot during the expansion and it bubbled up quite a bit. [...]Any ideas?


I've not used the Smooth-On foam, but the Tap Plastics stuff gets pretty warm too. Do you have a vent hole in the board on the bottom? (If not, I'd add one-- maybe ~3/4" or so-- and see how much foam comes out.) Maybe you've got too much foam and pressure/heat is building up and cutting back to 3oz or so might be better.

Do you have a rigid support shell around the silicone glove mold? (If not, the foam could just be exerting enough pressure to distort the mold at the weakest point.)


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## budude

Yes - I used the Plasti stuff to make the rigid form around the silicone mold. I do have a couple vent holes (besides the 1-1/2" pour hold) but they are pretty small - like 1/4" - mainly to ensure the air could get out. I will try a few bigger holes and perhaps a bit less foam mixture and see what happens. It's a bit like not getting the Christmas gift you wanted - spent all the time making the mold/shell and getting poor results makes it a little less fun... We'll see what happens - thanks for the advice.


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## havok1919

You might give Smooth-On's tech support a call too-- they're really good about helping out with troubleshooting their materials...


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## ashleyg2883

Hi, I'm new to the forum. My husband and I are going to try and make this. But he was keen to ask if you might consider making a mold for us and we'd pay you, and then we could go from there? Sounds silly, but I cannot find a good mold for sale on line and its almost absolutely going to happen that I'll mess it up if I try it myself.  

Thanks for reading!


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## StanFam3

One day I'd like to try my hand at this. You make it look so easy!


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## dassi87

I love this idea but I was always scared of the idea of making the mold. So I now ordered 2 molds from Etsy and hope I can do a ton of skulls fopr my party this year now.

If anybody is looking for molds like me, here is the shop.

If you are interested I will let you know how they are and how my skull turn out. =)


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## RCIAG

MMmmmmmchocolateskulls....mmmmmm


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## capn b

Could you do this same method with any plastic head form ? I thought about using one but changing up the facial features on it instead of making a duplicate


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## capn b

I'm interested in where you got the molds from as well as how yours turned out


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## capn b

Sorry mean to hit reply with quote. yes I would like to know where you got the molds from as well as how yours turned out


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## jHellion666

Great job. The replicas look so good. Im' using pretty much the same technique but I keep running into issues at the seams. The resin gets into the seam & kind of locks it together, then i break it trying to pry it apart. Are you using anything to shore up your seamlines?


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## havok1919

jHellion666 said:


> Great job. The replicas look so good. Im' using pretty much the same technique but I keep running into issues at the seams. The resin gets into the seam & kind of locks it together, then i break it trying to pry it apart. Are you using anything to shore up your seamlines?


Is your mold silicone? You could always give a quick spray with a mold release on anything that's 'sticking' (Pol-Ease® 2500 Release Agent or similar). With the relatively thick silicone (say, 1/8") layer and the exterior plastic shell holding everything tightly together I really didn't have any visible seams, but if got things mis-aligned it would leave a thing little line of flashing that easily broke away. I suspect that the best thing to do is figure out why the seam is opening and fix that first-- otherwise use some mold release so at least you don't have to fight it if it does leak some.

-Clay


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## jHellion666

Thanks for the quick reply. My newer molds are silicone, my older ones are latex. My question probably should've been, how do you get your seams to line up so well? I've been making a single seam line from about an inch above the eye sockets all the way down to base through the flange. I was under the impression that a flange was necessary, but I'm starting to get the impression that isn't the case. Any chance you could tell me where you make your seams? Your mold looks much cleaner than mine. I'm still fairly new to mold making, so forgive any dumb questions. I'm using my molds for roto-casting plastic resin.


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## havok1919

jHellion666 said:


> Thanks for the quick reply. My newer molds are silicone, my older ones are latex. My question probably should've been, how do you get your seams to line up so well?


What I did was to apply the silicone in layers and covered the entire piece like a glove-- then after it cured I cut back just enough so that I could pull the original out of the mold. I cut along the jaw line in sort-of a 'U' shape and then straight down the back of the skull (figuring that would be the least noticeable area were it to leave a seam). The mold is still one piece, but can be 'peeled' open with the mouth/eye sockets being the 'bottom' when it's filled. (Look about 2/3rds down the first page for my picture of the mold 'opened up'.) Since the silicone is relatively thick (~1/8"+), it's actually pretty rigid and wants to just spring back to the shape it was cast in which kinda automatically closes up the seams. Once the exterior support shell is in place it really holds the mold from all sides so it can't move around an allow any seams to pop open.


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## jHellion666

Thanks for the info. I really appreciate it.


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