To be read in conjunction with Resin Experiments as well as First Term Conceptual and Sculpey and 3D Modelling

This term I experimented with many different materials to form moulds.

latex (with corn flour)

alginate

plaster

silicone putty (builder’s silicone with corn flour)

silicone putty with latex

silicone mould rubber T-28

MouldStar silicone rubber

Mouldstar silicone rubber with thickener

Latex (with corn flour)

£15-ish

Last year I had already worked with latex (Love and Necessity) which has the following properties:

very runny— requires many layers

takes a while to set— especially if you have partially submerged an item in the latex and the layers are particularly thick

picks up detail well

deteriorates over many years.

So, I wanted to work with something a little faster and found that you could mix latex with corn starch to thicken it cheaply. I was hesitant at first, but it actually picked up the details very well.

I’d forgotten some of what I learned last year and didn’t consider the depth of the object I was making a mould of and added clay walls as an after thought. I made a seal by coating the after-thought of a clay border in latex.

I also flipped the mould upside-down and placed paper towels soaked in plaster over the top to give greater stability to the mould. Later I realized that Mod-Roc is a thousand times better, so I use that for everything after this point. Spoiler, I know.

Filling with resin:

I underestimated the amount of resin required and the edges of the leaf had picked up some of the clay I used to border the leaf.

I tried again, placing air-drying clay under my leaf and cutting around the shape of the leaf to make a mould.

I moved on from latex as I wanted something that picked up greater detail.

Alginate

properties of alginate:

runny

cures within minutes

safe to use on skin

deteriorates in about a day

great detail.

I placed a ring into a box and filled the box with alginate. I then had to carve out the ring a little, tidy up and fill with resin. The resin reacted quite strangely with the alginate: non-glossy surface with parts of alginate stuck to it. (see above)

Note, I try making a mould of this ring in a few different mediums below.

Alginate + Plaster

I made a mould of my hands by placing alginate in clasped hands and then attempted to make a cast from plaster. When I made the cast it was a struggle to remove the original alginate mould because of the under-cuts at the top. Of course I stupidly did remove it which meant that when I tried to use plaster as a mould for clay, I couldn’t remove the clay without breaking it because it went into those awkward undercuts.

properties of plaster:

inexpensive

heats up, do not use on skin

liquid/runny

inflexible

I didn’t use a lot of alginate due to the effect on the resin as well as the fact that the moulds don’t keep and that doesn’t seem very efficient for £7 a bag.

Builder’s Silicone (and Corn Starch)

£7-ish

properties of the putty:

difficult to get right

too sticky or not sticky enough

solid, not very flexible

picks up detail fairly well.

Having sculpted a 3D object, I wanted to make a 2-part mould to show off both sides. The first attempy was unsuccessful. I placed the object back into the mould and made some more silicone putty which I then also placed on top:

I purchased some silicone release spray (£5.86) to stop them from sticking together and still it wasn’t very successful. Also, the consistency of the putty in the first place was near impossible to get right. You could add corn flour so that the whole thing wouldn’t stick like gum to the object and lose all the detail or have a mess everywhere. I think this was my least-favorite thing to work with. I’d add water or oil as well and still it was in vain.

At this point I decided I’d cast what I already had and move onto another medium.

As mentioned earlier I tried casting that ring several times. I attempted a 2 part mould from silicone putty and latex and learned that they do not stick together which may come in handy later 🙂

(silicone poured into a box, with silicone and silicone thickener added to weaker parts of the mold.)

Silicone Mould Rubber T-28

£31.12

properties of the silicone T-28:

takes 24 hours to cure!

liquidy

picks up incredible detail

expensive.

I was still wanting to make a 2 part mould, so I tried again— this time with a different dinosaur.

This silicone require a lot of layering. I mean a lot. aaaannnd what’s worse is it took 24 hours between layers, so any progress was very, very, very slow. I decided to try mixing this silicone with some corn flour to make the process quicker and to fill in the under cuts. (In the image above and on the right there is a bright white and then a bulkier yellower-white. This off-white is the silicone mixed with the corn flour.

properties of silicone T-28 with cornflour:

not very flexible

solid/sturdy

cracks.

The silicone-cornflour mix was helpful when it came to adding a plaster layer. Since I had covered up all offcuts, the silicone was easy to remove from the plaster.

However, the dinosaur was not easy to remove from the silicone and I ended up snapping his horn off.

I think this was down to having so many points pointing in opposite directions. As you pull the item out of one side of the mould, you put pressure on the other. If the object could barely make it out, there was no point in casting as that too would break.

I started brainstorming ways of putting a mould together that would put the least tension on delicate points and decided that triceratops needed to retire and gave the stegosaurus a chance.

As I mentioned before, the silicone takes 24 hours to cure between layers, which means it all has sufficient time to drip completely off the object. I didn’t want to submerge the object completely in the silicone as 1) that uses a whole lot of silicone which can get pretty expensive and 2) making it very thick removes it’s flexibility which I need when there are so many delicate features and (our favorite) offcuts.

I did end up using this silicone for more sturdy objects later:

I also did this to test how efficient it would be to open the mould up by slicing once down the mould and shutting it back together with rubber bands. It works alright, but it would be better to reseal with silicone after every opening. (Some of the casts are pictured further down)

Some casts:

It was time to move on from slow curing silicone to the magical mystical Mold Star silicone:

Mold Star Series Silicone

A whopping £43.37

properties of the Mold Star silicone:

6 minutes working time, cures in 30 mins!!

expensive

picks up excellent detail

liquidy, but still viscous

This is after several layers, the difference is unreal. Because it cures quicker, the silicone doesn’t have as much time to run and the layers end up thicker than the other silicone. (You can see drops of silicone that fell so slowly they froze.) Also, not having to wait 24 hours between layer is awesome.

I removed the stegosaurus from the mold and repeated the process of sticking him in clay (the other side up) and coated him in several layers then removed him again:

Unfortunately, these two don’t match up exactly and aren’t cut in a straight line. Which is difficult for casting as liquid usually likes to lie flat and parallel to the earth.

I fashioned some plaster cases for the molds to sit upright and filled them with clingfilm so that I could make a smooth latex layer on the top so I could seal and possibly rotocast them.

Funnily enough, I did a bad job of filling the moulds with clingfilm and some latex managed to fill it. having a flexible mould and flexible cast made it really easy to remove and I’ll keep this in mind for the future.

Since the smooth covers turned out to be… not so smooth, I figured I would go ahead with casting to see how they turned out. (no photos for final result, see desk).

Original object next to cast:

For other objects I did the following:

applied several layers of silicone

used a crafting knife to clean up the edges

and occasionally had to put more silicone on after removing the object for thin places.

Some objects require more effort than others.

Crayons from Silicone T-28, everything else made using the Blue silicone:

Silicone + Thickener

properties of thickener:

thickens (obviously) — therefor sturdier, takes less time

loses detail

is not as nice to apply to delicate things as it has to be spread once applied.

Seeing as I’m impatient, I wanted to try adding thickener. This wasn’t just a time thing. Like with the guitar-pick above there are always thin spots which could break and then your resin leaks everywhere. It’s much more efficient to slab on a thick chunk of thickened silicone.

I tested this in different ways. On the necklace and the turtle I first did atleast 1 normal layer and then added a thickened layer. On the Stegosaurus, I just started off with thickener.

Removing them from the moulds:

Cleaning up the moulds:

Making them sturdier with a Mod-Roc sheets.

And finally casting:

That was the smart thing to do. Unfortunately I did not do the smart thing with the difficult, large and complicated object. Because the thickened silicone doesn’t seep into all the nooks and crannies, it looks a little sloppy. But it’s not a total loss because I’m still using this mould to experiment with forming the whole figure.

(Previously, I made two separate parts and tried to put them together. This time however, I coated the entire thing with silicone at once and used a scalpel to cut it into two parts— which I’ll cast into later.)

I removed the original before making the two plaster halves, which means the shape wasn’t very sturdy, so I filled it with tissues before adding the plaster sheets: