So you wanna make a silicone mold, but don't want to spend oodles of dollars on expensive silicone?
Well you are just in luck as I learned how to do such a thing when I got my fancy art degree.
Now this is a soft mold. So you probably don't want to be casting soft things in it (silicone, latex, etc.).
A general rule I follow (but as with any rule there are exceptions) is that you don't cast like into like, for example hard in to hard or soft into soft. So you don't make a plaster mold and then cast fiberglass into it. Unless you are making a one off mold and don't care that you'll have to break the mold to get the piece out. Conversely, casting silicone into a silicone mold is a bad idea. Why, you ask? Well silicone has this amazing property to stick to itself. So don't do it. Latex doesn't really stick to silicone, casting latex works better into something like porous so just use something like hydrostone or ultracal.
Here is what you will need:
-100% Silicone Caulk (If it isn't clear it's not 100% silicone caulk so ,you know, get clear.)
-Latex gloves (Make sure these are powderless. Powder + watery silicone = paste. You don't want that. Also, make sure that these are not silicone gloves. Silicone sticks to silicone very well. As far as Nitrile, I've never tried them.)
-Plastic cup (Use bigger ones than this. I spilled a lot of water. Tupperware works well too)
-1 caulk gun
Also something to make a mold of!
Now if you didn't make whatever you are making make sure you have EXPRESS WRITTEN CONSENT from whoever did. Make sure to give them credit too. For example, Garry Newton made this and I got his permission to make a mold of this for my mom. Don't just buy someone else's work and try to remake it and pass it off as your own. If you do this is called recasting and it is a terrible, terrible thing.
Anywho, I like to stick my items to something portable. This is a piece of sintra, but wood works too. That way I'm not confined to working in one area. Make sure you use something that doesn't succumb to moisture like cardboard does.
You will also need something to make a mother mold. I used hydrostone, but plaster and fiberglass work and they make a bunch of different materials specifically for making master molds. Master molds are used with soft molds so that when you are casting into the soft mold, the finished piece isn't deformed. A bad mother mold means that you get bad castings. Take your time with it. I didn't do a great job but do as I say, not as I do.
Now that you have everything, what do you do?
The first thing you want to do is put soap in the water. Use it liberally. It's better you put too much soap in than not enough. This is very important. The soap serves two purposes. The first is that it keeps the silicone from sticking to your glove. The second is that the soap acts as a catalyst and makes the silicone cure in about 15 minutes as opposed to 2 hours. I don't know why it does, but it just does. If you don't use soap, this process can take a whole lot longer.
Now that you've got the water all soapy, it's time to put on your gloves. I use one glove on my left hand (since I'm right handed) and I leave my right hand free to use the caulk gun.
Wet your glove with the soapy water. This will keep the silicone from sticking to your glove. Otherwise, you make a big, gooey mess.
Put a little less than a golf ball sized clump of silicone in your hand. I put it in my hand out of the cup so you could see a little better, but it's best if your hand is in the soapy water and the silicone goes into the soapy water before touching your glove.
Alternatively, if you have a wider container than this glass you can put it directly into the water and scoop it up. This is how I spilled most of my water, and I don't prefer to do this, but it does work if that floats your boat.
Wad your silicone into a small ball. Don't press too hard, it doesn't take much pressure. I've found it also works better to use a rolling method rather than a pressing one. What this does is it makes your silicone more manageable, but also ensures that there are no sticky parts of the silicone (showing that the silicone was fully coated in the soap).
After your silicone is sticking into a nice ball apply it to the surface of the object. Make sure that you don't apply it thicker than 1/8". This silicone cures when the acetic acid evaporates. If you layer it on too thick, the top layer will cure trapping a layer of uncured gooey silicone.
This is what happens when you put it on too thick. When you touch the surface you can feel that there is uncured silicone trapped underneath. It is much easier if you don't put it on too thick, but if you do I've found a pretty good solution. Basically, you lance the spot where it is wet and squeeze out all of the uncured silicone. You are then left with a pocket of air. This is very bad for molds. If you cut the top of the "skin" off so the spot that had the uncured silicone is exposed, you can take the uncured silicone and squish it back on (not too thick) and fix the pothole. Imagine lancing a blister and covering it with a band-aid.
Repeat for the second layer, thickening the mold.
This is the third and final layer. I used it to smooth out the mold and make it nice and form fitting. Normally this would be the layer where you would add keys for the mother mold, but this has a fairly distinct shape and I wasn't too concerned about the mother mold fitting on to the soft mold. Also, depending on the size of the object you may need more than three layers.
Now that the mold is ready for the mother mold, I built a divider so I can make a mother mold that will allow the final piece to come out. The reason for a two part mold is that this piece has undercuts. If I made a one part mother mold, I wouldn't be able to get the solid cast piece out of the mold so we make it in two pieces.
After both sides are done, you can pull out the original and you are done.
Voila! The rest of the images are of the mother mold and the original pulled out of the mold.
There you go. I spent all of 10 bucks to get all the stuff, and most of it will last for future use.
This method can get some pretty excellent detail. I would only recommend using this on smaller items, but it can be used on larger items. For example I used this method when I made these:
And of course there are pros and cons to this as with any method.
-Cheap in small batches
-Easy to work with
-Easy to obtain
-Good for small items
-More Expensive on a large scale
-Molds tear relatively easily (you could reinforce the silicone by adding a layer some burlap to the second layer while it is still tacky
-Since you are using soapy water, this method can trap water on the surface of what you are making. This is great if you are molding over plaster or fired clay, but less great if you are using dry unfired clay as the details can get washed away or if you use something non porous as water bubbles can get trapped on the surface of the mold if you aren't careful.
That concludes Mold Making, Cheap and Easy.
Until next time,