Have you ever had a glaze was too thick or too thin? Or perhaps it seemed to be just the right viscosity but it fired poorly.

Well, if you were at the hydrometer workshop, you know that  Harriet Hauser cleared up all the confusion. A hydrometer is a tool that will measure the specific gravity of a glaze and help you get more consistent firing results.

Once the proper consistency of a glaze is established based on firing results, the straw hydrometer is a simple and quick way to check that the glaze is mixed the same each time.

HOW TO MAKE A STRAW HYDROMETER

 

Adapted from an article by Roger Graham in Ceramics Monthly, June-Aug. 2013

Items needed:

• Plastic straw approximately ¼ inch in diameter Hot glue gun
• Lead or steel rod (or anything heavy that will fit inside the straw) Ruler with metric markings
• Fine tip Sharpie

Directions:

1. Fill one end of the straw with approximately ¼ inch of hot glue and allow it to set up:
2. Cut off a 4-5 gram piece of lead or steel rod and slide it down to the closed end of the straw (I like closer to 5 grams because it spreads the final measurements a bit.)
3. Place the weighted straw in a container of water and use a Sharpie to mark the level of the water. That will be 1.0 on the hydrometer.
4. Measure, in millimeters, the distance from the bottom of the straw to the mark made at the water level.

Divide the distance found in step 4  by 1.1, measure that distance on the straw and mark it as 1.1.

Divide the distance found in step 4  by 1.2 to get the measurement for the 1.2 mark.

Continue to divide the distance found in step 4 by 1.3-1.6 to obtain the other values.

Fill in the following Specific Gravity chart:

The Measurement from step 4 is a 1.0 and specific gravity of water.

Measurement from step 4 divided by 1.1 = ______________________________

Measurement from step 4 divided by 1.2 = ______________________________

Measurement from step 4 divided by 1.3 = ______________________________

Measurement from step 4 divided by 1.4 = ______________________________

Measurement from step 4 divided by 1.5 = ______________________________

Measurement from step 4 divided by 1.6 = ______________________________

Once the proper consistency of a glaze is established* the straw hydrometer is a simple and quick way to check that the glaze is mixed the same each time. Simply ease, not drop, the straw into the container of glaze; it should not touch the bottom, but float. Tap the side of the container a couple of times and note the level of the glaze on the hydrometer.

*  Do you like how the glaze looks on your pots after they are fired?

Prepared by Harriet Hauser