Tint etching

We may also use the method of tint etching to produce color contrast in microstructure. Tint etchants, usually acidic, are able to deposit a thin (40-500 nm) film such as an oxide or sulfide on specimen surfaces. Tint etching require a very high-quality polished surface for best results. Tint etching can also be done by heat tinting, a process by which a specimen is heated to a relatively low temperature in air. As it warms, the polished surface is oxidized. The oxidation rate varies with the phase and chemical composition of the specimen. Thus, differences in the thickness of oxidation films on surfaces generate variations in color. Interference colors are obtained once the film reaches a certain thickness. Effectiveness of heat tinting depends on the material of specimens it is effective for alloy steels and other non-ferrous metals and carbides, but not for carbon or low alloy steels. 

Klemm s I tint etch colors ferrite strongly also colors martensite and bainite, but not carbides or retained austenite. Use by immersion only until the surface is colored. 

Another technique (cumulative etching) permits a better differentiation of die phases in complex alloys, like Ti-Mp-Fe and Ti-Mo-O (26). The specimen (Fig. 10) undergoes several successive etchings for short times (0.3 sec.) under high voltage (125 volts) in order to develop thin oxide films of increasing thickness. The thickness, however, varies for the different phases. The best contrast of interference tints is obtained when the richest Ti-phase acquires a second order interference... 

Cubic or tetragonal crystals (NaCl lattice), d 2.78. mp 993 . bp 1704 , Poisonous Soly in water (g/100 ml) 4.0 (l5°) 4,3 (25°) 5.0 (10(f). Insol in ale. Aq solns have an alkaline reaction caused by partial hydrolysis. pH of freshly prepd satd soln 7.4. Aq solns etch glass, but the dry crystals or powder may be kept in glass bottles. Sodium fluoride sold as household insecticide must be tinted Nile Blue. LDW orally in rats 0.18 g/kg (Smyth). 

Aquatint a-kw9- tint, a- [I acqua tinta dyed water] (1782) n. Method of engraving which, like etching, involves the use of a mordant acid for biting a metal plate, but differing in that aquatint is used to render tonal instead of linear effects. 

Heat tinting is another type of deposit etch. Exposing a polished sample (not in a plastic mount ) to elevated temperatures in air causes oxidation to occur. On the microscopic level, oxidation rates of microstructural constituents vary according to their reactivity in a given environment. 

Protective top coat. This coating layer protects the metal from scratch, etching, and other deleterious physical and environmental effects. It must provide good adhesion to the metal and may be water-clear or tinted to provide different cosmetic appearances. 

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