Vulcan Black Coarse

Vulcan Black Stoneware is unlike any other on the market, providing an unusual intense brown-black colour when fired in an oxidising atmosphere. In a reducing atmosphere a metallic finish with shades of blue are obtained. Containing a coarse grog (up to 12 mesh) Vulcan Black Stoneware Coarse has been formulated especially for artistic ceramics. It behaves excellently during drying/firing and its high plasticity makes it ideal for modelling. It is widely used for murals and sculpture and is ideal for larger scale handbuilding. Supplied in a 12.5kg bag.

Typical Data:

• Firing range: 1200-1260ºC / Cone 5-7
• Biscuit temperature: 1000ºC
• Texture 8-9 on our indicative texture scale, smooth1, coarse 10.
• Water content: 21%
• Plasticity (IP Atterberg): 22
• Carbonate content (CaCO3): 0%
• Drying shrinkage: 7.0%
• Firing shrinkage (1260ºC): 3.6%
• Porosity (water absorption at 1260ºC): 9.8%
• Dry bending strength: 2.0 N/mm2
• Fired bending strength (1260ºC): 22.0 N/mm2
• Thermal coefficient (25-500ºC): 50.3x10^-7ºC^-1

(*) Firing range recommended for the clay to develop its best performance, both in terms of technical and safety characteristics, under conventional firing conditions. The colour samples may show temperatures outside the recommended range to provide a broader view, but these are pieces fired under controlled conditions.

TECHNICAL NOTES

Recipe Adjustment for Vulcan Bodies 2022/23:

From batch number 2322 (Production Week 23, 2022), due to unavailability of a raw material SIO-2 were forced to make an adjustment to the Vulcan recipe. Due to the high amount of grog, 164-VUC and VUX were not affected by the glaze thermal expansion sensitivity issues that affected older batches of 164-VUF and VUM. 

• Vulcan Black Stoneware (Coarse) is not recommended for tableware due to the grog content. Please see Vulcan Black Stoneware (Fine) instead.
• Vulcan is not toxic according to European Rules (CLP) and also American Rules (ASTM D 4236). The manganese dioxide content in Vulcan bodies is lower than 5%: Under the CLP regulation, the manganese dioxide content required for classification as toxic must be greater than 25%. 
• Vulcan Black Stoneware is no longer recommended for use in casting slips due to the high plasticity which makes it difficult to correctly deflocculate.

When glazing:

• Use zinc-free (Zn-free) glazes to prevent unexpected reactions such as bubbling or colour changes. Other elements that can react are zirconium (Zr) and tin (Sn). We have found that Mayco zinc-free clear glaze is suitable for use with Vulcan bodies and does not seem to suffer from the usual problems caused by outgassing from the high oxide levels in black bodies. Many ^6 commercial glazes such as Mayco perform well on Vulcan but trial-and-error is needed.