The type of clay you use to sculpt the mould for your prosthetic can really have an impact on your final piece. Different types of clay are great for different types of projects and terrible for others.
Basic Air Dry Clay aka Devil Clay
Basic Air Dry Clay is the easiest to get hold of as most art or hobby type of shops have it. It’s also pretty cheap. I used to use this to make my sculpts when I first started out but once I switched over to fancier clays I can’t go back to this stuff.
Generally air dry clay is not great for sculpting for prosthetics. It’s very soft, so it’s great for blocking out forms quickly, but when it comes to texturing and fine detail it’s a nightmare because just the tiniest amount of pressure creates deep marks. If you’re trying to do anything like loose flappy skin on a wound then it’s too soft to hold the form well, especially when you’re trying to get those really small gnarly bits. When you go to pour your casting material things like that can end up getting pushed down by the weight of the casting material.
Feather thin edges are a problem too. Air dry clay dries out quickly when it’s thin and it shrinks slightly meaning all those paper thin blending edges will crack as they dry unless you constantly spritz them with water to prevent them from drying out.
Because air dry clay dries out, you need to be sure that you’re going to be able to get your whole sculpt and cast done in a couple of hours which obviously for bigger or complicated pieces isn’t an option. You need to keep wetting the clay to prevent it from drying out and becoming crumbly and unworkable so you can only really use this clay if you know that you’re going to finish the piece within a few hours.
This clay can be great for building walls around your sculpts, although WED clay would still be a better alternative in my opinion because you’ll get much more uses out of WED clay than air dry clay and you can buy WED clay in bulk for cheap and air dry clay tends to be sold in relatively small blocks. It is a good option for anyone that’s just starting out and wants something cheap and easy to get hold of to play around with.
WED Clay – The Big Quick Master
WED Clay is also a water based clay, but there’s something added to it that makes it dry much slower (usually lanolin, glycerin or natural oils). Because of those additives you can work on a sculpt for about two weeks before it dries out. When you sculpt with this, at the end of your sculpting session you spritz your sculpt with water, cover it with a layer of wet paper towels, then wrap the whole thing in plastic to keep it moist.
WED Clay is soft compared to oil based clay, but it is harder than regular old water based air dry clay and it does start to firm up more over time.
Blocking out your sculpt is going to be fairly easy, and as it starts to firm up you’ll be able to add in the fine details like texture easily and be able to treat it a bit rougher than you would air dry clay. It’s a really nice sculpting choice, especially if you’re starting out and don’t want to deal with the quirks of oil based clay.
Because it’s a water based clay, you can use water to help smooth out the surface, buffing out tool marks and refining things.
Normally WED clay is used when you want to make really big sculpts in a short amount of time because it’s cheap compared to oil based clay and it’s nice to work with.
Oil Based Clay – The tricky mistress
Oil based clay is a dream and a nightmare to work with all at the same time. Because it’s oil based it doesn’t dry out, so you can keep reusing it over and over again. It comes in different hardnesses, soft, medium and hard but, even soft isn’t exactly soft, it’s like a brick. It is quite expensive compared to the other types, which is why WED clay is really the way to go if you want to make huge sculpts.
When you start your sculpt and want to block everything out you need heat up the clay to make it workable. You can even heat it up to a creamy liquid and drip/pour it on your work surface. As it starts to cool down again it hardens back up. This is part of what can make it tricky to work with, if you’re blocking things out and you decide to change something, then you might need to heat it up to get it soft enough to make changes. Basically, when you work with oil based clay you spend a lot of time heating things up to make it workable, or cooling things down to make it firm. When you start out with sculpting it can be a little tricky to get used to, but it is one of the things that makes this clay so amazing to work with.
When it comes to detailing and texturing, using a nice hard clay like this is a dream because you can be pretty rough with your sculpt and not worry about squashing parts of the form or making huge marks in the clay with a tiny amount of pressure. Pouring your casting material isn’t likely to squish any parts of your mould as well.
With Oil based clay, you can use naptha (lighter fluid) for smoothing and buffing surfaces, refining edges, getting rid of tool marks and things like that. Naptha is flammable and not good for your skin or inhaling so you need to be careful and work safely. You know, gloves, ventilation, mask, goggles, whatever’s going to keep you safe. You can use 99% alcohol as well, or I think turpentine although I haven’t tried either of those, I just stick with naptha.
Sulphur free isn’t a type of clay exactly, it’s like a subset of the types of clay, for example you can get sulphur free oil based clays. If you plan to be using silicone then you need to make sure you’re using a sulphur free clay because the silicone reacts with sulphur and can cause issues like the silicone not curing. There are ways around it like using sealers over your sculpt if you do end up using a sulphur clay but it’s easier to just get a non sulphur based clay.
Other types of clay – the mystery box
Monster clay has become popular lately which I haven’t had a chance to play with. It’s quite expensive and is a sulphur free oil/wax based clay. It’s used a lot like oil based clay with heating it up and cooling it down to make it workable.
There’s also a polymer clay Sculpey that’s becoming popular. Polymer clay usually doesn’t contain any clay minerals, it’s based on PVC. I haven’t used a polymer clay, but it’s very popular for making little clay models, beads and things like that. From what I’ve read it does dry out and get harder and you can fire it if you want to. There are ways to soften it back up while you’re working with it, but it seems like it’s not easy to re-soften like it is with oil based clays and requires you to massage something into it.
What clay should you use?
It can be really confusing when you’re starting out to know which kind of clay to use. My advice is to think about the project you’re doing, if it’s a huge sculpt that you’re going to be getting done in a week or two then WED clay’s probably a good way to go. Doing it with oil based clay would be expensive, and trying to control the temperature and softness on a huge piece would be a pain.
If it’s something that’s going to be sculpted over months, or if it’s something you’re just going to be working on on weekends and you don’t want to have to keep your clay moist then oil based clay would be a good way to go. Likewise if it’s a smaller piece then oil based clay is a good way to go. But, you could sculpt smaller pieces with WED clay, there’s no reason not to if you prefer working with WED clay.
If you can get your hands on different types of clay to play around with, then it’s worth it to try and find what works best for you and to figure out what you like to work with for different things. You might find you like doing more organic types of work with one type of clay, and more non organic pieces like armour with another type of clay.
Everyone has their own preferences so don’t feel like you need a certain type just because other people are saying it’s the best clay to use. It’s like anything, everyone develops their own favourites over time so try things out, see what you like.
I hope this was helpful guys, if you’ve got any questions or anything let me know in the comments section below and let us know what your favourite clay is and why.