CMC

Size: 25g

Carboxymethylcellulose to give its proper name is an organic compound. It is used in a variety of industries including food. When mixed with water it makes a thick liquid (a liquid with a higher viscosity).

We use it in our Vitraglaze range of brush-on glazes, with a water mixing ratio of 20g of CMC powder to 1 Litre of water. It's other main quality is that it will slow down the drying, which is what you want when you make a brush-on as it allows time for the brush marks to run and disappear.

It can also be used as an addition in dipping/pouring glaze as this will slow down the absorption of the water from the glaze into the clay body, making for a better glaze take up on a ware.

Things you should know about CMC

CMC is hygroscopic so it will absorb water from the air, both in powder form and liquid. Keep it well sealed from the air.

It is a perfect medium for growing life, put it into clean jars and keep it out of sunlight.
But if it does grow life, it will not harm a glaze although the smell would be unpleasant. You can solve this by adding a biocide, such as tea tree oil or an anti-microbial agent.

CMCs are different, there are many brands of CMC. Some have different strengths, particle/flake sizes and grades. If you have bought CMC from another supplier please seek their advice for their best mixing ratio.

Mixing CMC with water

Put your 20g of powder into a pan, add the water (1 Litre). Then bring up to a high heat on a hob, you do not want to boil it but almost get to that point, then turn off. If you boil the water you will lose water content and this will affect the calculation. Allow to cool and break up the clumps with a fork. Put a lid on the pan and let it absorb overnight.

Place in a sealed container, if possible one which is right for the size of the amount and do not keep for longer than a few days, so only make as much as you will need in the short term.

Making your own brush-on glazes

When you have mixed up the CMC with the water as instructed above, use the newly created mixture as your water ingredient in the glaze. A typical range for a powdered glaze is 700ml/800ml to a 1kg of powder. Each powdered glaze should be adjusted to suit your own personal application requirement and for the nature of the powder in the glaze. It is advisable to start at the lower end of the mixing ratio then increase as necessary. Don’t forget to sieve when thoroughly mixed.

• CMC SDS (PDF)