Glazes - measuring specific gravity

As part of my teaching about glazes, I also wrote a published article on the importance of keeping an eye on the water content of a glaze. The easiest way to do this is via measuring the specific grafity. So here we go:

Measuring the specific gravity of a glaze with a scale and a syringe is a simple way to understand its water‑to‑solids ratio and keep them consistent. I had learned to use the finger dip to get the glaze to the correct mix, but this can be unreliable, especially since some glazes like to be thick and others thin. Hence I started measuring the Specific Gravity (SG). If you are having problems with your glazes that could be put down to a high or low water content, this might be for you.

The finger dip method

Start by taring a syringe on your digital scale so it reads zero. Draw exactly 100 ml of well‑stirred glaze into it; making sure the glaze is fully homogenised, with no settled material at the bottom and take a reading of the weight. Because 100 ml of water weighs 100 g, the number you see on the scale is effectively the specific gravity of your glaze. For example, if the 100 ml sample weighs 145 g, the specific gravity is 1.45. Most of my glazes SG is between 1.35 and 1.5.

This method avoids the mess and inaccuracy of dipping hydrometers into glaze slurries and allows me to make sure a new batch of glaze is exactly the same as the one before and also measure/ track evaporation in the studio or from repeated use. I like to record the SG on my glaze container and measure before each use (but especially if the glaze was not used for a while). After a while, I got a feeling for each glaze and each recipe. I have some that like to be applied thickly with a high SG of 1.5 and others that still craze if applied at 1.42. The joy … !

Using Scales for measuring Specific Gravity

Test tiles for my transparent glaze