Stephani Stephenson on sat 13 apr 02
From research by Dr, brownell and other Ceramic Engineers at Alfred via
Ted Randall, Val Cushing....
From "Cushing's Handbook", 3rd edition
"To determine if your clay body is safe from cracking under freezing and
thawing conditions, find the C/B ratio by the following lab test
1. take a sample of your clay body and take the dry weight. You must
weigh carefully and accurately
Record this weight as D
2. Immerse this sample in water for 24 hours. DO NOT Boil the Water.
(just immersion, not boiling or heated water)
3. Take the saturated weight (after 24 hours in water)
Wipe off the surface water and weigh carefully.. Record the weight as C
4. Replace the sample in the water (immersed) and BOIL THE WATER. Leave
the sample in the boiling water for Two Hours
5. After two hours of boiling, wipe off the surface water and carefully
weigh the samples. Record the weight as B
6. us the weights determined above in the following formula:
D represents: Dry Weight of fired Test sample
C represents: WET weight
B represents Boiled weight
(1). C-D /D = 'C; value.(i.e., wet wgt minus dry wgt divided by dry
wgt gives "C" value
(Note that "C" value is different than 'C' weight above)
(2) . B- D/D = "B" value. (i.e., boiled weight minus dry wgt, divided by
dry wgt gives "B" value
(3). "C" value divided by "B" value = "C/B ratio".
The final result must be less than 0.78 to indicate that a clay body is
safe for outside use in winter, freezing and thawing situations.
This is the standard used in the Ceramic industry
Hope this helps