The Color Cobalt Blue Pigments Through The Ages

Although smalt, a pigment made from cobalt blue glass has been known at least since the Middle Ages, the color cobalt blue established in the nineteenth century was a greatly improved one.

The isolation of the blue color of smalt was discovered in the first half of the eighteenth century by the Swedish chemist Brandt. In 1777, Gahn and Wenzel found cobalt aluminate during research on cobalt compounds. Their discovery was made during experimentation with a soldering blowpipe. The color was not manufactured commercially until late in 1803 or 1804.

The Minister of the French government, Chaptal, appointed Louis Jaques Thénard and Mérimée to look into the improvement of artists’ colors. Thenard developed this new cobalt blue by his observations at the Sevres porcelain factory. He experimented with roasting cobalt arsenate and cobalt phosphate with alumina in a furnace. He published his results in late 1803-4 in the Journal des mines, “Sur les couleurs, suives d’un procédé pour préparer une couleur bleue aussi belle que l’outremer.”

Thénard tried the blue in oil and gum media and by the time his report was published, the color had not changed after a two-month exposure test. Production began in France in 1807. Most sources cited regard Thenard as the inventor of the blue. However, Leithner of Vienna is also mentioned as one who developed cobalt arsenate as early as 1775.

Cobalt blue was generally regarded as durable in the nineteenth century. It requires one hundred percent of oil to grind it as an oil paint otherwise its cool tone can turn greenish due to the yellowing of linseed oil. To avoid the yellowing, Laurie suggested that it be used as a glaze color or mixing it with white. It is totally stable in watercolor and fresco techniques. Field called it a “modern, improved blue”. John J. Varley, author of List of Colours, recommended it as a good substitution for ultramarine blue for painting skies.

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Porcelain Powder in the 21st Century

With the invention of powder coating about 60 years ago, a lot of work began in the coatings and finishing industries to leverage this new technology. The porcelain enamel industry was an early adopter of electrostatic powder coating, but a lot of development was required from both the material and equipment aspects. By the 1980s, porcelain powder coating was taking place in many factories, primarily for flatware but also in several lines for cavities, like ovens and dishwashers.

The physics of powder coating of porcelain powder is the same as for traditional powder paint, although there are some differences in behavior, etc. One of the most noticeable is the transfer efficiency; porcelain powder is about 40 percent efficient, so much more powder travels through the recovery system in comparison with traditional powder paint. Additionally, porcelain powders are often applied in a thicker film; usually six to eight mils. Almost all of the electrostatic dry powder porcelain enamel application is for major appliances; for exterior parts it is usually a two coat/one fire process, and for interior (non-appearance) parts it is a one coat/one fire process. In two coat/one fire processing, the first coat is a special ground coat enamel (designed to adhere to the steel) which is applied to a thickness of one to two mils, directly followed in a second application booth with a cover coat (for the final color of the part) at a thickness of five to seven mils. Both layers are melted/cured at about 1500 degrees Fahrenheit in a single pass through the furnace. Firing times are typically dependent on the thickness of the metal; for successful enamel coatings the time at peak temperature is two to three minutes.

For electrostatic powder enameling, the benefits are similar to powder paint systems. They include full recovery of overspray, coating thickness control, film uniformity, better edge coverage, gloss, and smoothness of finish after firing, plus the advantages of the automation and control of today’s powder application systems. The primary limitation for electrostatic powder enameling is the choice of colors; this is because the color must be smelted into the frit. The use of frit plus pigment is problematic due to differences in particle size, density, and electrical charging parameters – thus, recycling is difficult since the various constituents apply at different rates. Color change requires either multiple booths or significant clean-up time.

We have seen recent growth in the combination of robotics with powder application, which is improving production repeatability and efficiencies as well as reducing costs. R&D on electrostatic powder enamel chemical formulations and grinding technologies is also continuing with the objectives of improving application parameters and reducing defects.

This article comes from PCT edit released


Deep Sky Blue Transparent Frit

We offer frits, glazes, colours and raw materials for use in the various fields of ceramics like traditional ceramics, decorative tiles, enamelware and abrasive wheels.

Transparent frits are mainly used to formulate transparent glazes, crackle glazes and different colored glazes as required. These can also be used for making partially fritted glazes for 1150C – 1180C firing temperatures.

Transparent Frit Types :
Alkali Borosilicate
Calcium Borosilicate

This article comes from indiamart edit released

Direct on Enamel Frit

Enamel frits are the basic ingredient of porcelain enamel. Frit is most commonly a borosilicate glass and is formulated to incorporate desired properties like chemical resistance, heat resistance, color, cleanability, and more.

Enamel frit is made by melting raw materials together at about 2400°F (1315°C). The molten glass is quenched to provide flake particles that are used to make porcelain enamel coating.

This article comes from centerfrit edit released

Institute of Porcelain Enamel

Porcelain enamel (also called vitreous enamel or glass-lining) is an engineered boro-silicate glass layer, which may be applied in a liquid or powder form and fused on a metal substrates, like mild steel, cast iron, stainless steel, aluminum or copper.

This inorganic coating was already used by the Egyptians for art and jewels around 1000 B.C. and may be characterized by a number of unique chemical and mechanical properties, like :

  • Color stability (during many years)
  • Corrosion resistance (even against boiling water !)
  • Easy-to-clean
  • High temperature resistance
  • Scratch resistance

Porcelain enamel on mild steel (Also called ceramic steel or glass on steel) has been adopted by many different industries all over the world and is nowadays used for providing a functional and/or decorative coating to a wide range of products, such as architectural panels, bath-tubs, barbeques, boilers, chemical vessels, cookers, heat-exchange panels & tubes, hollowware, microwave ovens, street signs, water heaters, washing machines, etc.

This article comes from ditmer edit released