MEA CULPA! I FORGOT TO SET UP THE SCENARIO FOR THIS INFORMATION ON GLAZE AND COLOR DEVELOPMENT
I LIKE TO KEEP THINGS SIMPLE!
SINCE I NEVER USE GLAZE CALCULATION, I DON'T HAVE A LOT OF DECIMAL POINTS TO CONTEND WITH IN MIXING UP BATCHES OF GLAZE.
IF I USE SOMEONE ELSE'S CALCULATED GLAZE, I ELIMINATE ALL DECIMAL POINTS IN THE GLAZE RECIPE AND ROUND IT OUT TO THE NEAREST FULL NUMBER, OR, IN VERY SIMPLE GLAZES, DOWN TO THE NEAREST FIVE. I'VE DONE THIS FOR NEARLY FIFTY YEARS AND, WITH VERY RARE EXCEPTIONS, FOUND THAT IT MAKES LITTLE OR NO DIFFERENCE TO THE FINAL GLAZE. GET TO KNOW YOUR MATERIALS AND WHAT EACH WILL DO, THEN YOU CAN EASILY SUBSTITUTE OTHERS FOR SIMILAR OR DIFFERENT EFFECTS.
IF YOU DON'T LIKE ALL THIS ALCHEMY STUFF, YOU CAN ALWAYS FIRE WITH WOOD, SODA, SALT, RAKU AND PRIMITIVE FIRING. THESE FIRING PROCESSES ARE ALMOST GUARANTEED TO GIVE YOU A LARGE PILE OF SHARDS FOR A LONG PERIOD OF TIME! A GOOD, BUT EXPENSIVE LEARNING EXPERIENCE.
I SELDOM HAVE MORE THAN FOUR INGREDIENTS IN A BASE GLAZE, LESS IF POSSIBLE. USUALLY, THE MORE INTELLIGENT THE SELECTION OF MATERIALS, THE SIMPLER THE GLAZE AND THE FEWER THE POTENTIAL PROBLEMS. SIMPLE GLAZES MAY BE MADE FOR ALL REGULAR FIRING TEMPERATURES
I NORMALLY USE REGULAR COLORING OXIDES FOR COLORATION AND TEST THEIR SATURATION UP TO 10%. SATURATED COLORANTS OFTEN PRODUCE SOME INTERESTING AND UNUSUAL COLOR VARIABLES. OXIDES AND CARBONATES ARE NORMALLY MUCH MORE RELIABLE THAN UNDERGLAZES AND STAINS AND THEY ARE CONSIDERABLY LESS EXPENSIVE TO BUY.
I WILL WRIITE ABOUT OPACIFIERS AND COLOR MODIFIERS IN A LATER POSTING
GLAZES ARE USUALLY SHOWN IN THREE COLUMNS. ON THE RIGHT IS THE GLASSFORMER, ON THE LEFT ARE MOST OF THE FLUXES THAT MELT THE SILICA TO FORM A GLASS. IN THE CENTER IS NORMALLY CLAY THAT BONDS THE GLAZE TO THE CLAY BODY OF THE POT LIKE GLUE AND GENERALLY CONTROLS ITS FLUIDITY.
ALL THE GLAZE COLOR SQUARES SHOWN USE DIFFERENT SATURATIONS OF JUST ONE COLORANT IN VARIOUS TYPES OF GLAZE AND FIRING CONDITIONS. FULL INFORMATION IS IN MY BOOK, "THE CERAMIC SPECTRUM". THE SEVEN BASIC, COMMONLY AVAILABLE, MINERAL COLORANTS THAT I WILL BE TALKING ABOUT ARE: IRON, COPPER, COBALT, MANGANESE, NICKEL, RUTILE AND CHROMIUM. BETWEEN THEM, THEY CAN GIVE YOU ALMOST ANYTHING THAT YOU MIGHT WANT!
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THIS POST IS BROUGHT TO YOU
COURTESY OF THE COLORANT: COPPER
MALACHITE AND TURQUOISE, THE TWO MINERALS SHOWN BELOW, CONTAIN APPROXIMATELY THE SAME CONCENTRATION OF COPPER. IN MALACHITE IT IS FORMED WITH A MATRIX OF SILICA, AN ACIDIC MINERAL. IN TURQUOISE IT IS FORMED WITH ALKALINE MINERALS SUCH AS BORON, BORAX OR CALCIUM BORATE. THE FLUID PATTERN, LIKE OIL ON WATER, DEVELOPS DURING THE BOILING MAGMA STAGE IN A VOLCANO. IT HAS COOLED RAPIDLY AND IS IN A STATE OF SUSPENDED ANIMATION. IT HAS BEEN POLISHED TO REVEAL THESE PATTERNS AS GEMSTONES. BOTH HAVE BEEN FORMED AND COOLED IN CONJUNCTION WITH OXYGEN. IN SITUATIONS WHERE THE MINERALS ARE FORMED IN SMOKY CONDITIONS THEY WOULD HAVE SHADES OF PINK AND ORANGE TO RED, THE METALLIC OR REDUCED COLORS OF COPPER
MALACHITE
TURQUOISE
SOME OF THE COLORS THAT COME FROM COPPER
COPPER COMPOUNDS ARE CAPABLE OF PRODUCING AWIDE RANGE OF COLORS AND ARE VERY RESPONSIVE TO ATMOSPHERIC CHANGES, BOTH IN THE FIRING AND IN POST FIRING REDUCTION. THEY ARE ALSO ACTIVE FLUXES. IN LEAD OR HIGH-SILICA BASED GLAZES THEY USUALLY GIVE GRASSY GREENS IN OXIDATION AND A VARIETY OR REDS IN REDUCTION. IN BARIUM, STRONTIUM AND OTHER ALKALINE-FLUXED GLAZES IT GIVES TURQUOISE, BLUE-GREEN TO PURPLE. IN MAGNESIA-BASED GLAZES YOU CAN GET ORANGE PINK OR GREY. IN REDUCTION, COPPER CAN GIVE YOU LUSTROUS METALLIC SURFACES AS WELL AS VARIOUS REDS, PURPLES OF BLACK. COPPER COMPOUNDS ARE SUBJECT TO VOLATILIZING FUME ACTION AND MAY COLOR ADJACENT GLAZES CONTAINING TIN OXIDE. COPPER AND IRON ARE THE TWO MOST WIDELY USED COLORANTS IN THE CERAMIC FIELD.
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THE NEXT POST, ON FRIDAY 9TH, MARCH 2012, WILL LOOK AT THE POTENTIAL OF COBALT. COBALT MOSTLY GIVES THE BLUES.
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