Making test bars for the SHAB, LDW and DFAC tests

We will make bars of a clay body for the SHAB test (for shrinkage and absorption), a specimen for weighing wet, dry and then fired (to get water content and LOI) and a drying disk to measure drying performance and soluble salt content.

A. Insight-live

1
I'm going to demonstrate how to make our standard shrinkage absorption test bars from a plastic clay sample.
Rather than being a standardized test to produce absolute results, this is about simply doing things the same way each time to be able to make comparative tests of your own clays and clay bodies.
Start by cutting off about a kilogram of clay, and wedge it well with no air bubbles and no laminations. Then begin the flattening process in your preferred way - flatten it down to about twice as thick as needed.
Next, finish with a rolling pin. But rather than rolling it right down, repeat a cycle of rolling and turning it over. To get the right thickness use two 3/8" metal rods.

2
To cut to size use thin plywood boards (these are 4 1/4" wide). The bars are not disturbed after cutting, they are dried on these boards.
Cut each bar to 2.5cm, or 1" wide. Make bars for each temperature you intend to test for - at a minimum the target temperature and one cone above and below.
Stamp each bar with the code number assigned to the recipe in Insight-live and a specimen number (typically this is a single digit that matches the cone number). Finally, press a 10-centimeter mark using a length marker. We find that dipping it in talcum powder between each bar ensures a crisp mark each time.

3
For measuring the water content and the loss on ignition, cut a smaller sample, typically the same width as the bars, and 1 1/2" long. Round the edges, stamp the code number, weigh it and write that onto it using a needle tool.
Next, make a drying factor disk. Re-wedge the clay and flatten it as before - but this time roll it to 3/16". Like before, use metal guide rods to get the exact thickness.
Notice the wooden rolling pin - we find these don't stick as much as rubber or plastic ones.
This particular clay is quite sticky, so I have to be careful.
To cut the disk, we use a compass set at 6cm, thus getting a 12cm diameter disc.
Finally, put that on the board, stamp the same code number on it and place a plaster-filled can in the center.
The board is now ready to be put into the dehydrator.

Links

Tests	Shrinkage/Absorption Test SHAB Shrinkage and absorption test procedure for plastic clay bodies and materials

Video: Making SHAB, DFAC, LDW clay body test bars

This picture has its own page with more detail, click here to see it.

One-minute video. It demonstrates how to make the test bars for measuring clay body drying and firing shrinkage, fired absorption, a bar for measuring water content and loss-on-ignition and a disk for measuring drying performance and soluble salts content.

By Tony Hansen
Follow me on

Got a Question?

Buy me a coffee and we can talk