Instructables
Picture of Mold Making: Two Part Silicone Mold
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*UPDATE* I'm going to include some FAQ's to answer some of the questions I've received. { FAQ }


This tutorial will demonstrate how to reliably reproduce cast objects using a two part silicone mold. This technique, when skillfully applied, can have incredible resolution, effectively cast very complex shapes, and can yield parts that need little cleanup. This type of mold is most useful for parts that are fairly small, and therefore will not consume a massive amount of silicone to cast. To save material on large castings, techniques such as glove molding and matrix molding are often applied.
 
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Step 1: Select, clean, and add sprue

I chose a figurine from a comic shop as my demo to mold. This will be what is called the master. It has a fair amount of surface detail, and some small parts that, although tricky, are faithfully reproduced in the final casting.

Begin by inspecting, cleaning, and securing your model. I glued down the small parts that my figurine came with which originally snapped together. I took a cotton swab and got out all the grit and dust from every tiny crevice. Remember that everything you see on your part will be cast into the mold, even down to fingerprints. You will not be able to correct these mistakes once the part is cast, so take the time to do it right.

You will need to create a sprue or sprues on your part. These will become funnel shaped holes in the mold. You need them so you can get your casting material into the mold so don't forget to put them in. I usually use the tops to bottles or machine my own, but you can make most any tube or funnel shaped object work. If you'd like, you can even make your sprue out of clay. I usually smooth the seam in between the sprue and the master as to not catch bubbles on the very bottom of the part. Try to think ahead when you're molding a part, if something looks like it will trap bubbles, try to orient things to avoid it. Your goal is to create a mold that will produce the best quality parts with the least amount of work and fiddling.
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bluebel953 years ago
Can I use it to make cakes or gummy candies? :)

If you use food grade silicon and a non-toxic release, I would say that it would be perfectly fine.

Corn starch is used for gummies. Just spread the powder into a tray, press your master into the it and pour slowly into each cast. This is the method used at a candy shop I worked at some time ago. Once set, dump the whole thing over a screen and reuse the powder.
laudinetyme7 months ago

Great tutorial ... I have a question about making another type of mold. We make wax fake food and use Silicone as our molding material. I'm having trouble making a mold for a pile of something.....like a serving of corn, or hash browns...something that doesn't ordinarily come in one piece but I want to make a one piece mold using real food. Any idea how to stick real food together to be molds together? Any advice would be greatly appreciated...thanks My Email addy is LaudineTyme@aol.com if you want to contact me more directly....

shizumadrive8 months ago

I recognize that robot from Giant Robo! Thats one of the rarer ones.

rverdi1 year ago
oh thank you! I've been on the hunt for 'how to make mold' tuts lately!
rachel of OddModicum
http://www.OddModicum.etsy.com
blayze1 year ago
So ive sculpted an animal type figure and ive ran into mold problems. I want my seam to bisect it so i lie it in the box sideways but it buries the legs in silicone and i cant figure out how to not destroy the mold to remove it. Anything will help. Thanks
wilvic1 year ago
..this is great tutorial..thank you for this..

..i have few questions sir, if I'm going to use RTV, would the process be different?

and for example I'll make a mold of something that i created, let say from modelling clay, would you please suggest how i can make a mold of that?
ramses6 years ago
I only wish you could cast aluminum in it...
FYI there are additives to resin to give a metal effect ("metal cold casts")
frollard ramses5 years ago
You can cast many low-melt alloys into silicone - it can withstand many hundred degrees celcius; it can do pewter, or lead no problem. Not sure about aluminium.
Seriously watch out for moisture and water if casting aluminium. Ensure the mould is totally dry, and above 100 C, before a steam explosion ruins your day. Silicone won't take that heat from liquid aluminium, though.
Silicone should work with low-melt alloys; tin, lead, pewter...not sure about aluminium... it can handle temps uip to 588Kelvin (600F) aluminium melts at ~933Kelvin - definitely not a good plan. Good thought on the steam/water. Dry the mold, and pour slowly :D
Stop posting spam. Seriously. The reason the last account was banned was because you are not welcome here. Eff off.
Hi frollard,we are biggiest manufaturer in China and we can teach you how to make a mold and provide you free samples for testing.Pls contact me 0086 13790224736 or MSN:simonzhou520@hotmail.com
you could however take this mold pour melted wax in to it and make a wax master for lost wax casting. all you would have to do is add vents and set it in casting sand
Indeed - just wouldn't work for single-step processing. Damn I hate living in an apartment - i want so much to do so many...garage-y things.
Helos frollard5 years ago
I agree with you completely. I didn't realize until I moved into my own place just how necessary a yard and garage are. I also totally miss having a BBQ... Oh well, just plans for the future!
yea im kinda in the same position. i just made a vent hood and workbench in my place. not the safest idea but it works. i do small castings in the house.
that would be sweet
Rufo5 years ago
I have just made a rather complex mold of a sculpture I made in clay, the shell I made with plaster and it looked great, till I opened it and notice that the silicone was taky and stiky at some places... maybe the mixing went wrong is there something I can do, I can't afford to loose this mold... thanks
bofthem (author)  Rufo5 years ago
If your clay was plasticine, clasteline, or any other clay that contains sulfur you're pretty much screwed. The silicone has some cure inhibition when in contact with sulfurous material, meaning that it will only harden when it's removed from the clay and let rest with the mold open for anywhere from a few days to a few weeks. In the meantime, unfortunately, the mold will warp a little until everything cures. Depending on your model, this might not be an absolute disaster. There's a chance the silicone wasn't fully mixed, but that just puts you in the same situation. The only thing you can do to speed up the process is heat the silicone on a heating blanket or next to a radiator to get the catalyst to react faster. There's always a chance it just won't cure at all.
Hi dear friend,

Are you using RTV silicone for mold making?

We are biggest manufacturer of silicone rubber,we can provide you good quality with more cheap price and free samples for testing.

Pls reply me at : simonzhou520@hotmail.com

Thanks

Simon
Emphantasy Rufo4 years ago
 It also depends on what type of RTV silicone you used, tin or platinum.  Yes, products containing sulfur will inhibit platinum-based RTV, but I've yet to have that problem with tin, which cures against most anything.
Hi dear friend,

Are you using RTV silicone for mold making?

We are biggest manufacturer of silicone rubber,we can provide you good quality with more cheap price and free samples for testing.

Pls reply me at : simonzhou520@hotmail.com

Thanks

Simon
I'm looking to make soap molds and need a good supplier for the silicone, any suggestions?
Hi dear scottouradnik,

I know some good supplier who can provide good qulity with cheap price,hope can help you.Pls contact me MSN:simonzhou520@hotmail.com
hello, we are a professional manufacturer silicone rubber, contact me at my email hyjb@szrl.net. we can provide you most competitive silicone rubber to make molds for soap.
tinker2342 years ago
wow thanks
Sheilauva2 years ago
I am using window silicone, clear, sealant for my two part molds. I have not done this in 15 years and have forgotten what to use for a release, not for the clay, but for the seams around the clay. The silicone will stick to itself, so what do you use for the second half of the mold. Does this make sense?
Can I use canola spray on the silicone to release or vaseline, or do I have to buy a can of silicone release?
Traeh3 years ago
This is EXACTLY what I was looking for some small sculptures I wanted to cast in resin! Thank you for this awesome ible!!!
I have a pair of detailed flexible plastic wings that are curved. The wingspan is about 8 inches. Would this method work for them?
hello,this is Annie,you can contact with me more information about silicone rubber for making molds,annie7301011@live.cn.
I would like to know about your offer " information about silicone rubber for making molds"

Hernando Delgado Hdelgado2@verizon.net
 Hi.  If your master is really detailed, you might want to think about vacuum casting it- this process helps a lot with fine details.
how can i mold this: http://www.flickr.com/photos/14455307@N07/3804998669/in/set-72157618890095073/ i want it empty from inside
n0ukf5 years ago
Do you know of any casting materials that cure near crystal clear (like for lenses, etc)?
 I've used a lot of water clear urethanes from various companies- what they all have in common is that you'll need to use platinum-based RTV.  Tin based silicone has trace amounts of alcohol in it, which soft durometer urethanes/clears don't get along with.  Of course, you can also heat a tin mold or let it age naturally to get rid of the alcohol, but that takes time.
How long is the aging process and what temp. and length would would you need to bake it for. thanks ASAP
It depends a lot on the thickness of the mold...the thicker it is, the longer it takes to bake out the alcohol.  If the mold is 1/2 in thick, I'd guesstimate 90 degree F. for about 2 days.  I wouldn't go over 100 degrees F, because increasing the temp, while perhaps shortening the time needed, might also damage your mold.  Of course, this is done with the silicone fully cured, the master removed, and the mold laid out in the oven opened up, if possible.  Let the mold cool to room temp. before casting the urethane, and do a test shot if possible on the outside of the mold to check if the alcohol is gone before trying it in the cavity.  If the test shot is still tacky, bake some more.
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