TECHNIQUES OF APPLYING COLOR TO METALS

COLORING METALS SELDOM USES ONE APPLICATION UNLESS IT IS A TRADITIONAL FINISH SUCH AS A GREEN PATINA ON A BRONZE SCULPTURE. THE SURFACE IS OFTEN GIVEN DIFFERENT CHEMICAL BATHS THEN LEFT TO DRY FOR WEEKS OR EVEN MONTHS DEPENDING ON THE METAL AND THE COLOR EFFECT DESIRED.

COLOR CAN BE APPLIED BY USING: SCRATCH OR BRISTLE BRUSHING, PASTES, TORCHES, HEAT, VAPOUR, CLOTH, AND IMMERSION TECHNIQUES.

IRON AND STEEL HAVE VERY HIGH REFLECTIVE QUALITIES. BY USING A TECHNIQUE CALLED ELECTROPOLISHING, MICROSCOPIC DEFORMATIONS ARE REMOVED GIVING THE SURFACE A REFLECTIVE BRILLIANCE.

COLOR TECHNIQUES . . .

HEAT TINTING: A LAYER OF OXIDE FILM IS CREATED TO ACT AS AN INTERFERENCE FILM. COLORS RANGE FROM BLUE TO BROWNISH-BLACK. ALTHOUGH THIS METHOD PRODUCES RICH COLORS, IT CAN ONLY BE USED ON SMALLER SURFACES AND CAN TEND TO BE UNEVEN.

IMMERSION IN MOLTEN SALT BATHS: METALS ARE IMMERSED IN A BATH OF FUSED SALTS AND PRODUCES THE COLORS BLACK, WHITISH-YELLOW, MAGENTA, AND, GOLD. THIS TECHNIQUE IS USED ON SMALL ORNAMENTAL PIECES.

COLOR TECHNIQUES . . .

PATINA: THIS IS THE MOST COMMON APPLICATION FOR COPPER. PATINA OCCURS FROM THE COPPER SULFATE THAT FORMS ON THE COPPER THROUGHTOUT TIME DUE TO ENVIRONMENTAL CONDITIONS. PATINA CAN ALSO BE ARTIFICIALLY INDUCED. MANY FACTORS MUST BE CONSIDERED BEFORE USING THIS METHOD SUCH AS MOISTURE, TEMPERATURE, SURFACE AREA, METHOD OF APPLICATION, SURFACE OF THE METAL, AND DRYING TIME. THIS TECHNIQUE IS APPLIED CHEMICALLY USUALLY WITH A BRUSH OR A SPRAY. DIFFERENT VARIATIONS ON THIS SCHEME CAN CREATE BLACK, BROWN, RED, AND ORANGE ON THE GREEN PATINA.

TO PRODUCE A RICH BLACK THE COPPER IS IMMERSED INTO A BATH OF HOT CAUSTIC SODA(SODIUM HYDROXIDE) OR COPPER NITRATE FOLLOWED BY A COLD BATH IN POTASSIUM SULFIDE.

TO PRODUCE A RICH BROWN THE COPPER IS IMMERSED IN COPPER SULFATE AND COPPER OR SODIUM ACETATE.

COLOR TECHNIQUES . . .

ELECTROLYTE BATH: IMMERSING TITANIUM IN AN ELECTROLYTE BATH GIVEN AN ELECTRIC CHARGE WILL PRODUCE COLOR ON THE SURFACE OF THE MATERIAL OVER TIME. WITH CONSTANT VOLTAGE OVER TIME DIFFERENT TONES OF THE SAME COLOR APPEAR. TO CREATE A RAINBOW EFFECT THE MATERIAL IS IMMERSED IN THE SAME ELECTROLYTE BATH AND THE VOLTAGE IS ADJUSTED TO CREATE THESE VARIATIONS.

COLOR TECHNIQUES . . .

DILUTE CHROMIC ACID TREATMENTS: BY APPLYING THESE ACID TREATMENTS DIFFERENT HUES OF BLUE AND GOLD ARE PRODUCED. MORE INTENSE ACID TREATMENTS ARE USED TO CREATE PALE YELLOW-GOLD COLORS.

COLOR TECHNIQUES . . .

LEAD DOES NOT COLOR AS EASILY AS OTHER METALS. BY REMOVING THE OXIDE LAYER USING SANDPAPER AND BUFFING IT PRODUCES A BLUE-GRAY METALLIC SURFACE, BUT DOES NOT LAST VERY LONG. THE LEAD DEVELOPS AN OXIDE LAYER OF TARNISH IN BOTH INTERIOR AND EXTERIOR SETTINGS. LEAD IS BEST WHEN LEFT TO WEATHER ON ITS OWN AND IS USUALLY NOT USED IN LARGE SCALE PROJECTS.