TECHNO TIP: VARIEGATING GLAZES

While industry avoids so-called ‘reactive glazes’ (for consistency problems) potters avoid the ‘porcelain sink’ look and con- stantly seek ways to get glazes with sur- face variations in colour and texture. Here are some ideas on how to give drab glazes an exciting vari- egated or mottled surface.

Highlighting: Employ ‘highlights’ of the same colour but in a different shade. For example, vary- ing the thickness of a trans- lucent (partly opacified) coloured glaze will vary the intensity of colour (espe- cially where it thins on the edges of sharp contours). Variation can be achieved by pouring, double dipping, brushing, waxing, amd in- cising techniques,

Physical means: Create variegation by splatter-spraying or sponge-stippling asec- ond layer of glaze with a contrasting col- our of shade (or the same colour in a more matte or glossier version). A tngger or pump operated garden sprayer works well for this. Use a fluid glaze over a more stable matte (where spots tend to “feather” into the underlying layer) of vice-versa (where they tend to sit on top). While brightly coloured varicgated glazes look grew, subtle variations can be very effec- tive. An example is a glossy blue speckle or pattern on a matte blue background,

Surface Crystal Growth: Very fluid glazes are a must in forming crystals on the surface during cooling (low alumina, high flux). TiO2 materials like titanium dioxide and rutile seed crystal networks encourage their growth. A thin rutile wash applied to a glaze surface can act a5 a crystal growth catalyst. High calcium and boron encour- ages the formation of calcium-borate crys- tals, high zine plaxes also crystallize when they are Muid, The addition of up to 4% tin in such glazes can magnify the effect. Slow cooling greatly enhances crystal growth. Small amounts of lithium (e.g. 1%) can have a remarkable variegating effect on rutile glazes, especially when colourants like iron are present. Incustry

by Tony Hansen, Plainsman Clays Ltd

calls crystal growth on glaze surfaces “devitnification’.

Specking Agent: You can add acolounng oxide that contains particulate matter that speckles the glaze surface, Manganese granular, ilmenite, and granular rutile are examples but these materials are heavy and tend to settle in glazes that are too fluid. Ondi- nary iron oxide and cobalt oxide often produce small specks in unmilled glazes,

Multi-layering: Double layering of differem glazes produces variegation well when the lower layer is more fluid and the upper, stiffer glaze tends to break into islands revealing rivu- lets of the lower one. Be aware of the problems associated with double layer glaz- ing (cracking and crawling during drying because cither layer shrinks too much, is

applied too thick, or onto wet ware). Use glazes with lower or less plastec clay con- tent for multi-layered work and check out www.ravenscragslip.com,

Phase Differences: The glass matrix in a fired glaze can separate dunng melting forming globules of different glass chem- istry. These reflect light differently and thus variegate. “Techies” look for chemis- tries [hil encourage phase separation,

Combinations; Use combinations of the above to variegate surfaces even more. The popular Floating Blue recipe is a good example. [ts colour varies with thickness s© it highlights irregularities in the sur- face, Phase separation in the translucent matrix makes the colour ‘swirl’ in patterns of blue. Titanium crystals in the matrix make it sparkle. The growth of calcium- borate crystals on the surface appears to Noat over a deep bluc background,

Knowing the ‘mechanism’ of the variega- tion in your glazes is important to enhanc- ing and controlling them, and it will get the admiration of people who see your work.

CALL FOR SUBMISSIONS GRANVILLE ISLAND PUBLIC MARKET ANNUAL CRAFT ADJUDICATION

Craftspeople interested in selling their work at Granville Island Public Market should submit four samples on Sunday, February 18 9:00-17:00 1218 Cartwright Street on Granville Island, Vancouver, BC

Samples are judged in categories, depending upon items received.

Crafts NOT considered are clothing, crafts containing non-CSA approved electncal components, mass produced or manufactured items, kits or goods made from kits, imported goods and scented goods unless scent is enclosed.

There will be a $15 cash registration fee per category entered. Applicants will be setting up their own display.

For display criteria or other information please call Market Coordinator 604.666.6477 option #4

Potters Guild of British Columbia

February 2001