Step 3: Mixing and Setting

NOTE: The vinegar smell here is normal. Silicone caulking is mixed with acetic acid to help it cure. The fumes are harmless, but you will probably mix this outside.

To mix your molding material add the ingredients in the following order:

1. Measure out your Silicone into plastic cup (1oz)
2. Add appropriate amounts of Glycerin (3 drops)
3. Add appropriate amounts of Paint (1 Drop)
4. Add appropriate amounts of Mineral Spirits (.5oz)
5. Mix with plastic silverware until the paint is dispersed through the mixture with no white left. I like to use a knife, some prefer a spoon.
6. Scoop silicone into casting box. I say scoop becausethis material does not pour like molding silicone.  If you're trying to make a two part mold, you're going to have to add pressure to fill in the gaps.
7. Cure times depend on heat and moisture, but is generally 2-4 hours.

That's all there is to it! Follow the directions of some of the other casting instructables, and you should have a mold that you can make your own things with.
I found that using 2 parts cornstarch, 2 parts silicone caulk, and one part mineral spirits works well, more than doubles the ammount of molding stuff you get per caulk tube, and dries compleatley in under an hour. Not to mention, cornstarch is cheaper than caulk, so half the mold is cheaper. I haven't done a lot with it yet, but I have made some test molds which turned out excellent.
<p>How much mineral spirits do you put in a batch?</p>
<p>Is this substituting the liquid glycerine for the mineral spirits? </p>
<p>Sort of, you can use glycerine, instead or in addition to mineral spirits. Spirits has the advantage of being thinner, so less of it will make for a thinner silicone, however, if you add more than about a 2:1 silicone : spirits ratio, the mold will shrink when you're done. Glycerine does not suffer from this as much, if at all. </p>
<p>when i tried this it came out the consistency of floam (airy playdough). im not sure if this is right... i would like to know if this is the consistency that it is supposed to be. </p>
Roughly. I've usually found that a mixture of two parts spirits, one part cornstarch, and one part caulk usually turns out very airy and light, whereas the mixture mentioned above turns out more like a giant wad of rubber bands. Make sure that it dries fully first
<p>Update to this that I forgot to mention: you HAVE to use this type of mold quickly, you only get maybe a day's use before it starts to shrink. It will eventually end up about 2/3 to 1/2 the original size. Works fine if you just want to make something that looks nice, but not usable if it has to be a certain size. </p>
+1 to this mix. I tried the other mix but it took all night to cure. This one takes about 10 minutes to start to solidify and is done in 30. It is a bit thick, so I put some in a plastic bag(like a frosting bag) and apply it to all the detailed areas before filling in the rest of the mold.
Oh, also, despite the fact that silicone cures with water, adding water to the mixture will NOT help it dry faster, in fact, in multiplies the drying time erroneously. I made some a few days ago with one part water, mineral spirits, cornstarch, and caulk. It still isn't even surface-hard after about 4 days.
Yeah, I also found that one part silicone, one part cornstarch, and two parts mineral spirits will pour pretty well (but needs to be mixed with a drill-dremel), but it takes about 6 hours to dry. I just made an axe mould with it. Unfortunatealy, since the mineral spirits evaporate, it is very foamy, and though it still gets detail perfectly, it is much lighter and does not work well to hold up large molds. If you use that method, for a large mold (more than two inches or so) make sure to reenforce with fiberglass (I use house air filters, since cheap ones run as little as 50 cents. Also, MAKE SURE TO USE BREATHING PROTECTION!!
Do not use Silicone II. If it has gotten too cold or even frozen it will never cure. Use only 100% Silicone I. Only use acrylic paint. Because it is water based it can actually help to get water into all of the silicone. The over the counter silicone cures because of the moisture in the air. The point of glycerin is to get moisture inside the areas the air is not touching because it is harder for the silicone to cure once the outside has cured. I suggest using a little corn starch. It really speeds up the cure and makes the silicone harder when it cures depending on how much you add to your mixture. I have gotten very firm 2 piece molds doing that. Good luck!
<p>Deth, thank you for your comment. I gave up on these molds because mine never cured. Now I know the reason, I used Silicone II. I'll give it another shot.</p>
<p>You're scary welcome artdollist.</p>
<p>Hi there, Just a quick question, I have a mold for an adult toy (d...) to be filled with silicon, I d like to see if you guys can recommend me a type of product and if possible if i can give it a color skin would be very appreciated,</p><p>thanks in advance ! </p>
<p>Have you ever tried pure silicone that you put in a bowl of soapy water? I make a lot of my jewellery molds like this and I love it - it cures really quickly and lasts forever :D All you have to do is knead it under the water until it starts to get thicker and denser then all you have to do is form it in a ball, roll it out and press your items in it. I haven't tried it, but I bet you can cut a plastic cup in too, stick the top of the cup down, and pour it on top of the object. If you do this I would think that you shouldn't knead it as much so it's still soft enough to pour it over.</p>
<p>Hi,</p><p>I live outside the US, and I was wondering if I could use something else instead of the Mineral Spirits, since you can't bring it aborad and there's no exact equivalent here in my country (I've searched the internet). So, any suggestions for the thinning the silicone part? Thanks in advance</p>
<p>Mineral spirits is also known as Mineral Turpentine, in some places only as Turpentine. It's the most effective known material to use as a paint thinner, because it evaporates pretty quickly, leaving a thinner coat of paint that dries in a third of the normal amount of time.</p>
<p>I'm thinking perhaps 100% pure acetone (nail polish remover) would work as a thinner.</p>
<p>Lonecoon<br>Please post some pix of things you have made from your molds!<br><br>My two cents on &quot;Mold release&quot;.<br>For a mold release using epoxies I use Johnson's past wax. I've not had a need for a mold release agent while using silicone, yet. But, I would surly give it a try because a can of Johnson's past wax will last forever just using it for mold release.<br><br>If you do try the wax apply the wax two times to the mold before using the mold. Apply once and let it dry a few moments(ten to fifteen) and then apply the second time, and let it completely dry before using to mold.<br><br>I use epoxies to bed rifle barrels/actions into their wooden or synthecic stock. This gives a skin tight fit of the barrel to the stock which helps improve the accuracy of the rifle. To be able to get the barrel/action back out of the stock, and prevent the epoxy from cementing the barrel to the stock I use the past wax on the whole barrel, the screws and thing that the epoxy will be touching.<br><br>The fit between barrel and stock is so tight I have to use a mallet to pound them apart 99% of the time. The Johnson's past wax works great. I get a complete release of everything I apply the wax to. I too used mold release before I found out about the wax, and I spent a few bucks before, now it's just pennies!<br><br>From all the tests I've ran the wax has to be applied two time or more. Applied once will not work, I think it's because the epoxy gets really hot!</p>
<p>hi this might be a daft question but I got cornflour instead of cornstarch and wondering if I could that instead thank?</p>
<p>Be sure you don't buy the yellow cornflour which is lterally yellow corn flour instead of starch. 2 completely different things but appearently they have the same name in the UK. :)</p>
<p>Not daft at all. Cornstarch is what we in the US call it. I believe it is called cornflour in the UK and maybe elsewhere.</p>
what is the paint for?
The paint is to ensure that you get a proper mixture of your ingredients. Without the paint, It's much harder to tell if everything is properly mixed.
so basically, it's just for coloring... when it's all a uniform color, you know it's mixed well?
<p>yes you can see if it is mixed what a great idea </p>
Awesome! Thanks! Once the mold is set, is this able to handle heat, cold?? Can this be dishwasher safe and food safe? My intent for mold making is for decrative things around the home as well as for chocolates, cakes with fondont and for partys, to do ice, rice crispy treats, jell-o's and what ever else my brian has pop into it! Thank you for sharing!
I have no idea, as I've never tried. I can't say I'd recommend it, but I don't see why it wouldn't be food safe. Try it on relatives you don't like before serving it to party guests.
<p>what a joy to read your remark put some fun in my day laugh laugh</p>
<p>Do you have any data on how much heat/cold the finish mould can take, if its used for meltet plastic etc?<br>An can it be used for food-purpose like molds for cookies and icecubes?</p>
<p>I experimented a bit this morning with a similar silicone &amp; cornstarch recipe and was quite frustrated with the results. I'm happy to find here that a lot more glycerin and a lot less cornstarch may help solve the issues of setting WAY too quickly and firmly! I'll be trying again. Thanks for the ible and everyone's helpful suggestions!</p>
Sorry for asking... but, what are &quot;MINERAL SPIRITS&quot; ??? <br> <br>I does not live on USA, nor in english-spoken country (I live on latin america)... so... what is this? what is for? its a paint thiner?
<p>In Chile, it is called &quot;Aguarr&aacute;s&quot; or &quot;Trementina&quot;</p>
<p>But, maybe could be different... &quot;trementina&quot; comes as byproduct from pine resin... (as far as I remember)... and about aguarras, dont remember where it comes from...</p>
<p>Mineral spirits is a petroleum solvent product that is a mid quality thinner for oil based paints. Cheaper is &quot;paint thinner.&quot; Tops is turpentine. </p>
<p>Tks for the data... I learned a new phrase...</p>
<p>My first attept using the 2 parts White Silicone I + 2 parts Corn Starch + 1 part Mineral Spirit + 3-4 drops of Glycerine worked quite well! <br>I eyeballed all the amounts, next time I'll be more precise.</p><p>I still need to test the mold with model metal, and see if it resists the heat.</p><p>(54% Lead / 11% Tin / 35% Bismuth) Melts at 138&deg;C (280&deg;F).</p><p>Cast at 300-320&deg;C.</p><p>I was thinking about using lost wax technique to make the molds. I'll post my results.<br></p><p>Also I'd love to be able to pour the silicone rather than scooping it, to minimize bubbles. I'd love some reccomendation on how to achieve this. Maybe increasing the ratio of Mineral Spirit in the mix?</p><p>If it works, I can start creating my own metal figures and devices, and drive my wife nuts! :)</p>
I made this just using 100% silicone and paint thinner with acrylic paint for color mix 2 parts thinner to 1 part silicone...this will smell ....mix well till its thick gel liquid mix paint in as you are mixing...dont mix too much because you want this to be pourable...
<p>I have found that corn starch works the best. the more you use the quicker it dries. I have used a lot less than 1 to 1 mix and love the outcome. Try your own mix ( a little at a time) and see.</p>
nice technique ,but what about trapped air bubbles?... if you try to replicate a fine texture it would be better to spread by hand a thin layer of transparent (to be able to see eventual air bubbles) silicone caulking, also keep your hands wet (dip in soapy water) so the silicone doesn't stick to your precious fingers :-)
<p>A thin brush works, too. If you wipe off the excess goop straight after you've finished painting your part you can use it quite a few times. After the mixture sets you can also get the goop out by running a metal trowel over it a few times.</p>
How well does this process actually work. will the silicone dry all the way through even if it is thicker than 1/4 inches?
<p>Cornflour/starch will make the mixture set all the way through. The more you use the faster the silicone will set. About half to one part of the starch/flour to one part silicone is about right. Any more and the stuff will set while you are mixing it. </p>
I've made molds that are an inch thick with this recipe, with no problem. The glycerine is the key to making sure it dries all the way through.
Other good sources of pigment are mineral color, which masons put in mortar.. OK, you don't want a 20-lb sack of color? Try the chalk powder meant to go in snap-string line which is sold in hardware stores and comes out of a ketchup type squeeze bottle. Art stores may also have powdered pigment so your casting can be an exact hue. <br>
<p>Chalk and plaster of paris and gypsum will fast set your silicone. Don't use them. If you use colorants try minerals that do not interfere with setting time.</p>
Can you use side walk chalk that is for kids? Also to make homemade chalk it's craft paint and grout powder. Can these be used?
I tried this recipe and my mold is still gooey 2 days later.. What am I missing? Here's what I did:<br>3 oz of silicone, <br>9 drops glycerin, <br>3 drops paint, <br>1.5oz mineral spirits.<br><br>I poured (scooped really) it into a wood frame about 1 inch tall, 2 inches wide, and 4 inches across. I also made a small glob (maybe half an ounce) off to the side which also hasn't cured yet. <br><br>I had it in my garage for the first day and I thought maybe it was too cold or humid, so I brought it inside and it still hasn't cured after another day.
<p>You are missing the essential cornstarch. This sets the mixture all the way through, not just where it is in contact with the air, or close to it. You need half to one part cornstarch to each part of silicone, optional drops of paint, optional drops of glycerin and one to two parts of mineral spirits or paint thinner. You just used the wrong formula. Try again.</p>

About This Instructable




More by Lonecoon:Using Silicone Caulking to Make Molds 
Add instructable to: