•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
pH (pugged clay) - pHPG
This test procedure was employed in the Foresight Ceramic Database and now is available for those having an account at Insight-Live.com.
Accumulating test data using the variables defined in these procedures enables us to create tools that enable you to compare the physical properties of materials and recipes.
A measure of hydrogen ion concentration. This test is only comparative if samples have the same solids percentages and are prepared the same way. If this number is quoted it should specify the % solids in the suspension or solution (e.g. 4.8 @ 10% solids).
The pH of most clay suspensions lies between 4 and 7 indicating they behave as weak acids.
The pH aids you in understanding the amount and type of additives to obtain desired viscosity, especially if producing a slip. Variation in pH is also a contributor to variation in a pugged body's tendency to soften or stiffen with storage; examination of historical pH data along with observations will indicate direction on compensating by varying water content or additions of epsom salts, vinegar, etc. to the mix.
This test is designed to measure the pH of a solution prepared from the clay and water used in production each day.
2.1 Test solutions are prepared mid-stream on each production run by the pugmill operator.
5.1. Take or Make the Sample (Pugmill Operator)
5.1.1. Midway through the run take a 25 gram sample of powdered clay and 100 gram sample of water. Stir clay into water for 1 minute. Set timer for 1 hour.
5.1.2. When timer sounds, dip pH meter into water to immerse the bulb and record the reading in logbook.
5.1.3. Clean meter and container.
5.2.1. Scale for weighing powder sample.
5.2.2. Measuring container for water.
5.2.3. Stiring rod.
5.2.4. Facilities to wash and clean container.
5.2.5. pH meter with calibration solution.
5.2.6. Timer with audible alarm.
5.3.1. Do not breathe clay dust unnecessarily.
5.4.1. Be careful to get a representative sample in the middle of the run.
5.4.2. Use a water sample from the source feeding the pugmill.
VAL - Value (V)
The pH value measured as described in the procedure.
TYPE - Value (V)
This indicates whether the test was done on a sample of POWDER or PUGGED.
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By Tony Hansen