Enamel opacity

Crystalline opacity in lead glasses can be evolved by means of AS2O3 in amounts corresponding to 3 — 8% the compound Pbj (As04)2 is formed in the glass. It produces a strong enamel opacity suitable for flashed glasses. 

China Porosity 10-15% Firing temperature 950-1200°C Enamel, opacity Sanitation, tile Refractories, and Glasses... 

Fluorosis affects the enamel of the tooth, causing it to become hypominera-lised. This is detected as visual changes in the opacity, and it is only in extreme cases that this leads to an adverse appearance as mottling of the tooth surface [86]. The severity of the discolouration depends on the dose of fluoride, its duration and timing of consumption. 

Common Earthenware or Delflware is characterized by its extreme opacity, jta open porous structure, and soft texturo in fracture it is earthy, and always colored, while, instead of a transparent glaze, it is coated with enamel. 

In the field of glass, ceramics, and enamels, ZnO is used for its ability to reduce thermal expansion, to lower the melting point, and to increase chemical resistance. It can also be used to modify gloss or to improve opacity. 

Enamelling consists of forming an adherent glass on the metal surface. Surfaces treated in this way are resistant to attack from acids and weak alkalis. The glasses may be coloured and formed into decorative patterns for household ware and jewellery and are prodcued from a mixture of oxides of silicon, boron, sodium, calcium, and lead. Secondary elements are also added, e.g. nitrates and manganese dioxide, which oxidise impurities, other oxides to aid adhesion to the metal surface, and pigments to impart colour and opacity. 

This fluorspar contains 85-95% CaF2 and is used as a flux in the steel industry, production of enamel glass to control refractive index and obtain desired opacity. It is also used in coatings of welding rods. 

Brill (6) summarized the information on the chemical basis of medieval glass colors as follows red/orange opaque enamels, cuprite (Cu20) with lead additions beneficial for opacity white opaque enamels, either tin oxide opa-... 

A glaze is defined as a thin layer on the surface of a ceramic product,either glassy or partially crystalline. Its main function is to render impermeable the surface of a porous body, to permit application of decoration techniques, and in some cases to improve the technological properties. In contrast to enamels, to which glazes are related by their naturp as well as function, a lower degree of opacity is usually required and transparent glazes are frequently employed. 

White enamels are currently obtained by so-called recrystallization opacity ... 

Inhibitive Pigment a pigment which retards or prevents the corrosion of metals by chemical and/or electrochemical means, as opposed to a purely barrier action. Red lead and zinc chromate are examples of inhibitive pigments as opposed to red iron oxide which has little or no inhibitive action. Medium in paints or enamels. The continuous phase in which the pigment is dispersed thus in the liquid paint in the can it is synonymous with vehicle and in the dry film it is synonymous with binder (q.v.). Opacity (Hiding Power) ... 

Opacity. Defined in ASTM - C286 as The property of reflecting light diffusely and non-selectively. For a definition relating specifically to vitreous enamel... 

White Ground Coat. Term sometimes used for a white vitreous enamel of high opacity used for one-coat application. White Hard. Clay from which surface water has evaporated. 

Cobalt Blue n (1835) Co0-Al203. Pigment Blue 28 (77346). Bright blue pigment, which is a complex product derived from oxides of cobalt and aluminum. It has excellent lightfastness and good chemical and heat resistance and with low opacity. Density, 4.2-4.3 g/cm (35.0-35.8 Ib/gal) O.A., 27-36 particle size, 0.5-1.0 pm. Syn Azure Blue, Cobalt Aluminate, Cobalt Ultramarine, Dumont s Blue, Enamel Blue,... 

When used in lead-bearing enamels, a yellow color may be produced by the formation of lead antimonate. Also, antimony oxide does not give as good opacity in leadbearing enamels as it does in the leadless types. 

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