- Lesson details
In this video lesson artist and mold maker Matt Lewis will teach you how to build a simple box mold using a disposable plastic cup. You will learn how to make the easiest box mold possible including techniques, materials and tools, as well as how to cut the silicon and create the partitions in the mold.
- Plastic Cup
- Utility Knife
- Ballpoint Pen
- Foam Core Board or Cardboard
- Hot Glue Gun
- 2 1/2 Quart Buckets
- Digital Scale
- Mold Max 30 Silicone Mold Making Rubber
- Paint Stirrer
- Latex or Rubber Gloves
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In this video lesson, artist and mold maker Matt Lewis will teach you how to
build a simple box mold using a disposable plastic cup. You will learn how to make
the easiest box mold possible, including techniques, materials, and tools. Matt
will show you how to cut the silicone and create the partitions in the mold, and you
will leave with a complete, start-to- finish understanding of this approach.
Hi, I'm Matt Lewis. I'm going to be walking you through the steps for
making a simple box mold using a paper cup, or in this case, a plastic cup. We're
just going to be making a mold off of a very simple figure, so there are not
going to be a lot of vents or anything like that involved in it. We're going to
be using silicone rubber. It's a tin-based silicone that we won't need any mold
release or anything like that. So, essentially, all we're going to need
to do is cut the top off the cup, fit the figure inside, and fill it up. So, I think
we're ready to get started.
OK, we're going to cut the top of the cup out, and that's going to give us a spot to
pour the rubber in. So you take an X-Acto blade or a drywall knife and carefully
cut a small opening. Just go slow so you don't cut yourself. You don't have to come
all the way to the edges or cut the entire lid off. That gives you just enough opening
to be able to pour it in. I'll make sure everything is clear on there. And that
looks good. Before we glue it down, you want to make sure you register where
you're going to cut the seam when you take it back apart. On this particular
piece, I want to come up the back in the least obtrusive spot. I don't want to cut
into anything important – across fingers, the face, or anything like that. This piece
also doesn't need to be cut all the way around, so I'm probably just going to come
partway up the back, maybe up onto the neck a little bit, but not quite to the ear.
So I'm going to take a regular ballpoint pen. I can register a line right where I
want to cut that. You can make a little note on the board if you need to. This
line will register in the rubber, so when you pull the rubber off, you'll see that
line registered on it. OK, we're ready to glue the cup on. And for that, I'm just
using regular hot glue. I'm going to put a couple of drops on just to hold it down.
Give that a minute to cool off. You may need to hold it for a second, or if you
have a weight to hold it down, you can do that as well.
It's always a good idea to have a couple extra hot glue sticks handy so you don't
have to let go of this and go running for your hot glue.
OK, that feels pretty good. I'm going to run the bead all the way around.
It shouldn't need a ton of glue on there, but you want to make sure that the bead
makes contact with the cup and the board.
And just hold that down until it cures.
OK, that feels pretty good. Once the glue is cooled off, he'll be ready for silicone.
All right, I'm ready to pour my silicone here. So before we mix it up, you're
going to need a bucket and a scale that can measure enough rubber to pour into
your piece. This is a tin-based Shore 30 silicone, which is 10-to-1 mix. So you're
going to have 10 parts of silicone to 1 part of the catalyst. I've got my scale
here that I'm going to set to grams. I have some pre-poured stuff, so I'm
going to measure the weight of the bucket and then replace it and tear it out with the
pre-poured rubber. OK, I'm going to take this off and replace it with the rubber.
This is 1200 grams, so I'm going to put 120 grams of the catalyst in here. So tear
out your scale.
All right, and that'll do.
Now, you need to mix this thoroughly before pouring it in. You can also vacuum
the air, which pops all the bubbles and gets all the bubbles out of it, so when
you pour it, there won't be any bubbles trapped against your piece.
OK, we've got our silicone good and mixed up and ready to pour. So you want to
pour it lightly over the edge of the bucket. And try and find the straightest shot
to the bottom of the cup. You don't want it to have too much turbulence when
you're pouring across the figure. On this one, it'd be nice if it can hit him on the
back and kind of fill from there. If you pour slowly over the edge of the bucket,
it sort of pops the air bubbles as it goes if you have to too much air entrained in
your rubber. Just a slow, steady stream is good. And if you have any spots on your
part that look like they're going to catch air or be an undercut, if the piece is
small enough, you may be able to rock it to one side or another and make sure
that spot gets filled. On this one, there's a little negative space behind the front leg.
I'm just going to tip this thing back and let the rubber come up in gradually
behind the front leg. And then, as it fills in, I'll just slowly put it back down.
You want to fill in about an inch above your figure. You don't necessarily have
to go all the way to the top of the cup, but it is good to get at least a half-inch
to an inch above the part.
Now, once it's filled, it's a good idea to have your hot glue gun still
handy with extra glue sticks and check to make sure you're not catching any
leaks around the edge at the bottom. This one looks OK, but if you do see it start
to come through, you can just put a dab of glue on there and it will not only cure the
rubber, but it'll stop the leak.
All right, I let this rubber sit for 24 hours to get nice and cured, so I'm
ready to de-mold. I've got a couple of knives here. The first is just a drywall
knife and I'm going to use this just to cut it out of the container. The second
one is a scalpel that I'll use to make my jeweler's cut into the rubber down to the
part inside. I'm going to start out with the carpenter knife. I want to cut through
the hot glue, and you can cut through the paper as well - through the foamcore.
You're just going to peel that off. I'm going to peel it all the way around. You
don't need to be concerned about saving your cup; whatever cup you use, I'm sure
you'll be able to find a duplicate. I've got an extra one here, so we can cut
through this cup. But you want to be careful not to cut into the rubber. I'm
going to make a little cut right on the side just so it comes loose off there.
If you used a paper cup, you can tear it away. This is a plastic cup, so you may
need to make a couple of cuts on here, actually. Again, like I said, you want to
be careful not to cut into the rubber itself. There we go. I'll make a couple
of cuts around the edge. I'm just going to kind of work it loose as you go. With
a clear cup, you can see the surface tension releasing on the inside where
it's coming loose.
I'm just going to go ahead and peel this cup off. You can also use waxed paper
cups for this; it makes it a little easier to get it out.
All right, I can discard those. Now, the original line we made on the foamcore
registered into the rubber, so you can see that line that I made with the
ballpoint pen. So get the rest of the paper off the bottom. You can just
peel that flashing that seeped underneath our original part. I'm going to use my
scalpel. You don't want to cut too much into the rubber, but I'm just going to
take a little bit of this flashing off. Now that I can see the edges of the
part inside, I'm going to make my first cut. There's a key knife that you can make
with a groove that would cut all the way up the back, or cut any of your seams,
but I'm going to make a jeweler's cut, which is just a zig-zag cut. I start right
on my seam and around the corner. And I'm only going to go about halfway up. And I
want to cut all the way to my part on this first cut. Now I can come inside and cut
to the piece in here. You want to make short, deliberate strokes – you don't want
to make too long of a cut because you might cut into the piece itself, or you
might make a double cut, so it helps if you have an extra set of hands or someone
to hold it open. But if not, you want to make these short little cuts all the way
up your original cut. Once you get to the piece, you want your cut to be as straight
OK, that looks pretty good. Now I'm going to make my straight cut.
All right. Now that I've found the figure inside, I can see where I want to follow
my line. Straight up the back. And you want to find the cleanest spot you can
possibly cut through. Obviously, you don't want to cut through any faces, ears, eyes,
nose, anything like that. Anything with a lot of detail. So you want to find a nice,
clean spot and make that straight cut as high up as you need to go. For this
particular piece, I don't need to go all the way to the top. It's fairly small; it
should work itself out. I can just kind of flex it around. I've got a couple of
deep undercuts on here, so I'm going to kind of work the piece around. If you
have to take the piece apart to get it out, it's always best to do it. The mold
is now more important than the original part. But if you just go slow and kind of
stretch back and forth, you should be able to work any of those little undercut pieces
out without tearing them. I'm going to bring this up just a little higher up the
back. So, again, make your zig-zag cut and then just short strokes all the way up, as
high up as you need to cut. I'm going to try and stop right there. I'd like to stop
before I get to the head. It's small enough to where it should come out
of there by itself. Now, I can see a spot right here that's a catch behind the leg,
so if I can stretch it out far enough, I can make that cut right where I need
to. Another way to do it would just be to pull the piece out and let the clay come
apart as you pull it out.
All right, so there's our original part. And I lost a leg in there – it's still in
there – but now I can come back in and I can cut right down the middle of the back
of that leg. And I've got an even amount of rubber on either side of it. Depending
on what the original part is made of, if it's water-based clay or something like
that, you may have to come back in and scrub it out. But this is an oil-based clay
that was fairly hard, so we've got a pretty clean mold that doesn't need much
cleaning. And that's pretty much ready for casting, so I'm going to take this
clean cup that we have and I can just drop that right back in. It should lock
in. You may need a mold release or something like that if it's sticking a
little too much.
It's ready for casting.