Conditioning means preparing the clay to ensure that the manufactured ingredients are well mixed and evenly distributed ready for use.
Why is conditioning clay important? The main reason for conditioning is because, if the ingredients are not thoroughly and evenly distributed, then this may result in a weak and brittle clay once it is cured. Conditioning also has the added benefit of making the clay softer and easier to work with.
Polymer clay is comprised of polyvinyl chloride (PVC) resin and a liquid plasticizer plus a range of fillers, binders and pigments which change the opacity, colour and characteristics of the clay. Generally, it remains workable until heat is applied. In other words, it does not dry out but is ‘thermoset’ which creates a chemical reaction causing the polymers to link together to become into a solid.
Illustration © Lizzi Bucklow-Holt 2019
Over time, some ingredients of raw clay will settle or ‘sink’ or even evaporate, making the clay appear to be hard and crumbly. Some old clays can be revived to a usable state, so don’t despair! It will just take some time and patience.
It’s unlikely that you will be able to use any brand of clay straight out of the packet, so it will need to be conditioned before you start making your creations. Yes, it can be tiresome, especially with stiffer clay brands, but I promise it will be worth the effort!
First, it helps to get the clay warmed up. Have you ever had toffee from the fridge? It’s hard and brittle, isn’t it? But it you leave it out on a warm day, it goes soft and gooey. Well, raw clay acts in a similar way. But we’re talking about bringing it up to body temperature, not much more. Simply hold it in your hands for a while, put it under your arm pits, or even sit on it (wrapped of course)! Don’t be tempted to microwave it or put in hot water. Patience is the key, so get the clay warming up while you prepare your work area.
Next, we need to get the clay moving. Start by rolling, flexing and twisting it back and forth. Cut the clay into manageable sized pieces if that helps. The movement helps to activate the molecules and warm up the insides of your piece of clay too. At this stage, some people like to hit the clay with a hammer too which is great for stress-relief! Others use an adapted arbor press (like the Never Knead) to squash whole blocks of clay.
Photo by Dan Bollinger
By now the clay should be feeling like it’s ready to stretch. Roll it into a log, fold it and repeat a few times. Try to avoid introducing air pockets. It should become easier and easier to manipulate. The test to see if it is fully conditioned is to roll it out flat and thin. If the edges remain smooth, it’s fully conditioned. If they don’t, keep on folding and rolling. TIP: If you have a pasta machine, you can use it to condition the clay once it has been warmed up. Do not try to put cold clay into a pasta machine, as you will likely damage the internal cogs, and that’s a whole new problem to deal with!
My clay is really crumbly, what can I do?
Chop up the clay into really small pieces, then pass it through a pasta machine (PM) on a really thin setting. The very small gap applies a lot of pressure, squashing the clay pieces together. Keep running it through the PM, adding more crumbs as you go until it is all stuck together and conditioned.
Fiona Abel-Smith shows this technique here in a video she kindly made for the Guild.
"Nope, it’s still crumbly!"
In this case, it’s probable that the plasticizers have leached out and need to be reintroduced. The best thing to add here is a little clear liquid polymer clay. Again, cut the clay into tiny pieces, put it in a plastic sandwich bag and drizzle a little liquid clay over it. Seal the bag and manipulate the clay to mix it. Leave it 24 hours and then try conditioning it again. You can also try adding mineral oil (such as baby oil) which helps to soften the clay but use it sparingly as too much can weaken the structure of the clay.
It’s still grainy and not conditioning after all that! Argh!
Then sadly it’s probably a lost cause. It might have been left somewhere considerably warm, near a radiator perhaps, and it's partially cured. However, rather than throw it away, chop it into small pieces and add a small amount to scrap clay to use as bead or armature cores. That way it won’t go to waste and you can be environmentally conscious. Don’t add more than about 10% or you might weaken your creation.
Advanced tip 1: It is recommended that freshly manufactured clay should be stored for at least six months before use. Usually the manufacturer or distributor will do this for you, not releasing the clay onto the market until it is ready. But it has happened before and people complain that it is too gooey. It just needs time for the composition of the clay to bind together. If you understand the batch codes, you might be able to work out how old your clay is.
Advanced tip 2: translucent clays may be conditioned in a slightly different way as they can be prone to 'placquing' or 'mooning' whereby small opaque bubbles or crescent shapes seem to appear in the clay. Ginger at The Blue Bottle Tree, goes into more detail here, but one way is to cut thin slices from a warmed, manipulated (but not folded) block of clay and run it through a PM at a very thin setting ONCE.
How do you condition your clay?
What tips do you have for conditioning?
What tools do you use?