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Barnard Slip
High Iron Clay
Chemistry
Chemistry available on new site, see link above
Links to Other Materials
- Albany Slip - Unspecified
- Ravenscrag Slip - Unspecified
- SG 758 - Substitute
- Cache
Miscellaneous
- Family: Clay Other
- Region: North America
- Mined At: Unspecified
- Raw Mineral: No
- Generic: No
Notes
Barnard clay has long been used by potters as a source of iron in dark firing glazes. It offers price advantages over using iron oxide and being a clay aids in suspending the materials in the slurry. Barnard has proven valuable for iron slip glazes requiring high clay content. For example, a mixture of 90% Barnard and 20% calcium carboate will produce a nearly black glaze around cone 9.
The chemistry appears to be highly variable. We have seen iron amounts as low as 14% and as high as 34% (the other oxides are likewise variable).
However, it is a silty material with very low plasticity; so low that it is difficult to form test specimens from it in the plastic state. The material is extremely messy to work with an stains containers and everything it touches. There is some variation in the color and thus fired results of glazes and slips employing it.
This is one of the most stained clay materials available.
Fired bars are very dark brown at cone 02 proceeding to black at cone 4.
At cone 6 it is beginning to melt.
To duplicate this material the base clay needs to have low plasticity and be high in iron and silica and low in alumina and flux. Since iron oxide and silica need to be added flux containing clays could be diluted enough to work. If you would like more information please email us and we can give you trial recipes in return for your reports on their testing.
Data
- Drying Shrinkage: 3.8-4.2% @ 25% water
- Water absorption
Cone 04: 10.4%
Cone 2: 2.5
Cone 3: 1.3
Cone 4: 0.6 - Firing Shrinkage
Cone 04: 11.5%
Cone 2: 15.7
Cone 3: 16.2
Cone 4: 15.5
Cone 6: 15.6 - Melting Point (MP): 2100F
- Sieve Analysis Wet
on 60 mesh: 0
120 mesh: 1.0%
200 mesh: 5.0% - Melting Point (MP): 2100F
- Firing Shrinkage
Cone 04: 11.5%
Cone 2: 15.7
Cone 3: 16.2
Cone 4: 15.5
Cone 6: 15.6 - Water absorption
Cone 04: 10.4%
Cone 2: 2.5
Cone 3: 1.3
Cone 4: 0.6 - Drying Shrinkage: 3.8-4.2% @ 25% water
Suppliers
- Hammil & Gillespie
Authors
- Tony Hansen (Owner)
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