Crackle Glazes

These are the glazes that contain a pattern of hairline cracks. These cracks are sometimes deliberately produced for aesthetics. These are incorporated by adding higher concentrations of alkali metals. From the firing temperature, the coated ceramic is fast cooled to get a fine pattern. 

Celadon, tenmoku, raku, and copper glazes are examples of crackle glazes. 

Celadon glazes were produced 3,500 years ago. The color of the glaze varies from light blue to yellow and green. The different colors are obtained by adding Fe203 in concentrations of 0.5-3.0 wt%. 

Copper glazes may contain up to 0.5 wt% CuCOg initially. On firing, CUCO3 decomposes to CuO. The furnace atmosphere is filled with CO to reduce CuO to Cu. Thus, the glaze contains copper particles in it. These copper particles give a red color to the glaze. 

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Crackle glass has been produced for its artistic appearance for over 150 years (perhaps since the sixteenth century in Venice). The glass is heated to 1000°C and then plunged into water causing cracks to form across the surface if reheated and blown further the cracks heal on the interior a similar effect is produced in glazes. ... 

Crackle. (1) A multiply crazed or cracked surface on art pottery or glass. To produce the effect on pottery the glaze is compounded so as to have a higher thermal expansion than the body the craze pattern is sometimes emphasized by rubbing colouring matter, such as umber, into the fine cracks. With glass, the ware is cracked by quenching in water it is then reheated and shaped. (2) A crackled vitreous enamel - the... 

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