MATERIAL GUY - PART 3

WEDNESDAY, 29TH FEBRUARY, 2012



PART 3 - "ROCKS IN THE HEAD!"

MY SEVERAL "SECOND HOMES" DURING MY CHILDHOOD INCLUDED ALL OF THE MUSEUMS IN THE PART OF LONDON CALLED SOUTH KENSINGTON. THESE INCLUDED THE NATURAL HISTORY MUSEUM, THE SCIENCE MUSEUM, THE VICTORIA AND ALBERT MUSEUM OF DECORATIVE ARTS AND, LAST BUT CERTAINLY NOT LEAST, THE GEOLOGY MUSEUM. IT WAS THERE THAT I FIRST BECAME OBSESSED WITH ROCKS AND MINERALS AND THEIR MYRIAD VARIATIONS OF COLOR AND TEXTURE. I CAREFULLY LOOKED AT ALL THE LABELS ON THE SPECIMENS. THEY STARTED WITH A DESCRIPTIVE NAME SUCH AS SODIUM FELDSPAR OR TURQUOISE, FOLLOWED BY THE MINERAL CONTENT WRITTEN IN CHEMICAL SYMBOLS. I CAME TO REALIZE LATER THAT THIS WAS EXACTLY LIKE A GLAZE RECIPE. I CAME TO PREFER TO UNDERSTAND CERAMIC MATERIALS FROM THEIR GEOLOGICAL ORIGINS RATHER THAN THEIR CHEMISTRY. ALL THE INFORMATION IS IN THOSE LABELS.

A FEW COPPER CONTAINING MINERALS

MALACHITE  (ACIDIC)

TURQUOISE (ALKALINE)

CUPRITE - FORMED IN REDUCTION

RAW COPPER

VARISCITE

I STARTED TO REALIZE THAT A PIECE OF BISQUE-FIRED POTTERY IS ACTUALLY A CHUNK OF SIMULATED, POROUS ROCK. THE GLAZE THAT IS PUT OVER IT IS A COMBINATION OF OTHER ROCKS, POWDERED AND, WITH THE ADDITION OF WATER, MADE INTO A LIQUID. THIS LIQUID IS APPLIED TO THE BISQUE AND THE WATER EVAPORATES. ON FIRING TO A SUITABLE TEMPERATURE,  IT TURNS INTO A SKIN OF GLASS AND FUSES TO THE CLAY, BECOMING FOREVER BONDED. THIS SAME PROCESS HAS BEEN UTILIZED BY MANKIND FOR 4,500 YEARS, ALMOST ALL OVER THE WORLD EXCEPT IN PERMAFROST OR HUMID JUNGLE CONDITIONS WHERE THE CLAY WILL NOT DRY ENOUGH TO BE FIRED WITHOUT EXPLODING FROM THE WATER CONTENT THAT TURNS TO STEAM WHEN HEATED. A ROCK IS GENERALLY A COMBINATION OF SEVERAL MINERALS. A CERAMIC MINERAL IS PURIFIED AND DECONTAMINATED. THE SELECTION OF THE DIFFERENT ROCKS AND MINERALS TO MAKE COLOR AND GLAZES IS A LENGTHY, CUMULATIVE, RESEARCH EXPERIENCE, LEARNING BY TESTING AND OBSERVATION. GLAZES WERE BEING MADE BY TRIAL AND ERROR FOR OVER FOUR THOUSAND YEARS BEFORE THERE WAS A CHEMICAL EQUATION BASED UNDERSTANDING AND GLAZES COULD BE CALCULATED PREDICTABLY.  MY PREFERENCE IN GLAZE AND COLOR DEVELOPMENT IS BY EMPIRICAL MEANS OF LEARNING MATERIAL BEHAVIOR UNDER THE EFFECTS OF HEAT.

RUTILE CRYSTALS IN A MATRIX OF QUARTZ (SiO2)

WHEN YOU LOOK AT CRYSTALS IN NATURE AS ABOVE, IT BECOMES EASY TO UNDERSTAND WHAT THEY DO IN GLAZES.  RUTILE IS IMPURE TITANIUM, OR TITANIUM WITH IRON. THE MORE THAT YOU LOOK AT MINERALS, THE MORE YOU CAN VISUALIZE THEIR POTENTIAL IN GLAZES.  MOST CERAMISTS BUY POWDERED AND PURIFIED COLORANTS. THE IMAGE BELOW SHOWS WHAT WE NORMALLY USE. THE IMAGES ABOVE SHOW A SMALL VARIETY OF WHERE THE POWDERED COLORANTS COME FROM.

PREPARED AND PURIFIED OXIDES AND CARBONATES

CLOCKWISE FROM TOP: COPPER CARBONATE, MANGANESE DIOXIDE, COBALT CARBONATE, RUTILE, PRASEODYMIUM STAIN, RAW UMBER, AND RED IRON OXIDE IN THE CENTER.

ANY BASIC GLAZE IS A COMBINATION OF THREE THINGS, SILICA - WHICH FORMS GLASS AT AVERY HIGH TEMPERATURE; A SERIES OF FLUXING COMPOUNDS - THAT LOWER THE MELTING POINT OF SILICA, AS WELL AS CONTROLLING THE COLORATION POTENTIAL OF COLORANTS: AND ALUMINA - THAT ACTS AS THE BONDING MECHANISM  BETWEEN THE GLAZE AND THE CLAY THAT IT COVERS. SOME OF THESE MATERIALS ARE ACIDIC AND AFFECT COLORANTS IN ONE WAY. SOME ARE ALKALINE AND AFFECT COLORANTS IN ANOTHER WAY.  THE FINAL RESULT OF ANY GLAZE IS THE RESULT OF ANOTHER THREE THINGS.  FIRST, THE COMBINATION OF MATERIALS THAT MAKE UP THE GLAZE. SECOND, THE TEMPERATURE AT WHICH IT IS FIRED.  AND THIRD, THE ATMOSPHERIC CONDITIONS IN WHICH IT IS FIRED.  TO THAT BASE,  ONE ADDS COLORANTS AND OPACIFIERS TO ROUND OUT AND COMPLETE THE GLAZE AS DESIRED.

WULFENITE: LEAD COLORED WITH MOLYBDENUM

WHILE I REALIZE PERFECTLY WELL THAT NOT EVERONE HAS A MUSEUM OF GEOLOGY AND MINERALOGY ON THEIR DOORSTEP, THERE ARE MANY MINERAL AND ROCKHOUND STORES AND THE WILD AND WONDERFUL WORLD ORF NATURE. OBSERVE WHAT IS THERE AND IMAGINE HOW YOU COULD USE IT.

MALACHITE IS BASICALLY SILICA FUSED WITH COPPER IN A VOLCANO AND COOLED IN OXIDATION.  THE PATTERN IS CAUSED BY BOILING AND BUBBLING MATERIALS CAUGHT AND COOLED IN A STATE OF ARRESTED DEVELOPMENT.

WITH A GOOD FOUNDATION IN GEOLOGY, AND THE EARLY REALIZATION THAT A  CERAMIC GLAZE IS JUST A THIN COATING OF VARIOUS ROCKS APPLIED TO THE CLAY SURFACE, I SET MYSELF UP WITH A RESEARCH PROJECT THAT LASTED OVER TWENTY YEARS. THE PROJECT WAS TO REALLY UNDERSTAND CERAMIC GLAZE AND COLOR, AND WHAT EVERY MATERIAL CONTRIBUTED TO THE MIX, HOW THEY REACTED TOGETHER AT A NUMBER OF TEMPERATURES IN EITHER OXIDATION OR REDUCTION  FIRING. I WANTED TO GET TO KNOW MY MATERIALS SO WELL THAT I COULD LOOK AT ANY COLOR IN ANY SITUATION AND COME UP WITH A GLAZE RECIPE AND COLORANTS NEEDED TO GET IT.  SINCE I WANTED TO APPROACH THE CERAMIC SURFACE AS A PAINTER, THIS METHOD SERVED ME WELL. IT ALSO LED TO MY FIRST BOOK ON SIMPLIFIED GLAZE AND COLOR DEVELOPMENT "THE CERAMIC SPECTRUM", STILL GOING STRONG AFTER NEARLY THIRTY YEARS.

I DON'T USE GLAZE CALCULATION TO DEVELOP GLAZES.  I WILL ELABORATE ON WHY IN MY NEXT POSTING ON FRIDAY, MARCH 2ND.