LOI/Density/Water Content - LDW
Procedure
1.
Purpose
This test measures water content, LOI, and density all from the same test specimen. It should be done using small samples which are big enough to stamp and write weights on, but small enough to be able to weigh on a scale designed to provide the ability to suspend objects under water. Density is measured on the principle that water buoys up an object by a force equal to the weight of the water it displaces. That means the difference between the weight of an object in air and under water equals the weight of the water it displaces. Since water weighs 1 gram/cc, the difference is also the objects volume in cc.
L.O.I. is expressed as a percent loss in weight. This figure is derived by preparing clay bars, drying thoroughly above the boiling point, weighing, firing past sintering, (about cone 04) then weighing again, and calculating the percent loss in weight. This loss in weight can be due to organic material in the clay (coal, wood etc), water of crystallization, and the liberation of various gases by chemical processes taking place on heating. Different types of clay minerals have different LOI's. (ie. Kaolin loses 13-15% of crystal water) A typical L.O.I. for a native pottery clay is between 4 and 8%. If the bulk of weight loss is from coal and carbonaceous matter, problems like pinholing, pitting of the surface, and black coring in reduction can result (black coring causes weakening and changes in thermal expansion). Ball clays are commonly high in carbon and organic content. Keeping an eye on LOI helps to note differences in mineralogy, likelihood to pinhole or bloat, and tendency to produce fumes during firing.
It is best to intermesh the procedure for this test with the SOLU and SHAB tests, making the specimens for each at the same time.
Related information on the theory, purpose, procedure and interpretation for this test is available in the Magic of Fire II book.
Variables
H2O - % Water (C)
Wet Weight - Dry Weight / Wet Weight * 100
LOI - LOI (C)
Dry Weight - Fired Weight / Dry Weight * 100
DENS - Grams/cc (C)
Oil Weight / (Oil Weight - Immersed Weight)
WWGT - Wet Weight (V)
Enter the weight of the freshly prepared sample. This should have been written on the sample when it was made.
DWGT - Dry Weight (V)
Enter the weight of the sample after thorough drying. This should be written on the sample in ceramic pencil. It is important that the specimen be dried for several hours in at 100C+. Failure to do this can easily result in 0.5% errors.
Very fine clays (i.e. mix of 10% raw bentonite with 90% calcined bentonite) can have a water content of 40%. Coarser clays will have good workability at 18-20%.
FWGT - Fired Weight (V)
Enter the weight of the specimen after firing. Specimens must be fired to a consistent temperature, i.e. cone 06.
OWGT - Oiled Weight (V)
Enter the weight of the specimen after it has dried after being immersed in a liquid the will prevent water absorption during weighing under water (i.e. silicone sealant, wax emulsion, brick or concrete sealer).
IWGT - Immersed Weight (V)
Enter the weight of the sample under water. When weighing, be sure the scale is zeroed, the sample is completely under the surface, and no air bubbles are trapped on its lower surface.
Out Bound Links
- (Tests)
SHAB - Shrinkage/Absorption
In Bound Links
- (Articles)
The Physics of Clay Bodies Learn to test your clay bodies and recording the results in an organized way and understanding the p... - (Tests)
BLOI - Borate LOI
- (Tests)
CLWC - Clay Water Content - Powder, Plastic
- (Tests)
LOI - LOI (100-1000C)
- (Tests)
MOIP - Moisture Content - Powder
- (Tests)
DENS - Density (Specific Gravity)
- (Tests)
WSR - Wet Sieve Residue
- (Articles)
Formulating a Porcelain Understanding the functions of each of the major materials in a high temperature porcelain gives you...
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