Measuring the Specific Gravity of a Ceramic Glaze Using a 100 ml Syringe and a Digital Scale

Measuring the specific gravity of a glaze determines the amount of water you have in the glaze and, therefore, provides a numerical measurement of glaze thickness. This is helpful when trying to recreate glaze effects that depend on a certain thickness. 

1. Using a clean 100ml syringe, weigh the empty syringe and “tare” the scale. This means zeroing out the scale so that it reads “0” grams.
2. Dip the tip of the syringe into the well-mixed glaze. Pull the plunger up about a quarter of the way, then depress it again while still in the glaze – this helps purge the air in the nozzle. While the syringe is still in the glaze, draw the plunger up to precisely the 100 ml mark.
3. Dry off the tip of the syringe and weigh it again.
4. Record the weight. It is usually between 125 and 160. This is the weight of the water AND glaze. Remember, 100 ml of water weighs 100 grams.
5. To get the specific gravity, divide the weight by 100 (easily done by just moving the decimal point two spaces to the left). For example, if your syringe with 100ml of glaze weighs 135 grams, this glaze would have a specific gravity of 1.35.

What to do with this information:

• If the specific gravity is too low (the number is low), the glaze may be too thin. Let sit overnight and screen some of the water off after it settles.
• If the specify gravity measurement is too high, the glaze may be too thick (add more water).

In this example, the scale reads 132 grams after the empty syringe was tared on the scale. So, this glaze has a specific gravity of 1.32.

Mackenzie White = 1.42
Horsley’s Satin Matte White = 1.30
Steve’s Copper Red = 1.56
Rutile Blue = 1.45
Rutile Green = 1.45
Iron Saturate = 1.38
Temple’s Persimmon = 1.29
Liz Kraus Shino = 1.37
Jeff’s Long Beach Blue = 1.54
IUS Celadon = 1.41
Monica’s Seafoam = 1.35
Cushing’s Satin Matte Black = 1.39
Missouri Straw Yellow = 1.21
Hensley Clear = 1.46

The different materials and recipes of each glaze make for different specific gravity readings, so while the above numbers fall within a spectrum, there is variation from glaze to glaze. Specific gravity is also preference – some people may want a particular glaze to be thicker or thinner for different effects. Additionally, while testing glazes, it’s a good idea to record the specific gravity when you have a color or surface you like (so that you can repeat it later).

One advantage the 100ml syringe has over using a hydrometer for measuring specific gravity is that you only need 100ml of glaze. When you use a hydrometer, you typically need much more glaze to get an accurate reading.

Measurements over the past few semesters ….