Review Sheet for MSE 257A at UA
Review Sheet for MSE 257A at UA
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This 3 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 12 views.
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Date Created: 02/06/15
Glazes 1 What is a glaze a a continuous layer of glass coating the surface of a ceramic 2 Processing a b raw ingredients collected ground fritting optional i purpose make glaze ingredients insoluble in water avoid ef orescence and poisoning ii fusionmelting of ingredients together upon cooling they form a glass breaking up into small particles grinding iii sintering of ingredients reacting in the solid state at high temperatures grinding application i to dried unfired body or ii red unglazed body bisque iii in a slurry particles suspended in water 1 dipping brushing spraying iv drying ring i can done in one or several steps depending on the properties of the glaze the temperature at which it becomes liquid ii temperature has to be quotjust rightquot 1 if too high the glaze will ow too much low viscosity and collect in pools 2 if too low the glaze will not completely melt and ow over the rough surface of ceramic body 3 often glazes have to be protected from the combustion gases of the fire which contain CO ashes etc saggers are used 4 care needs to be taken to prevent pieces from sticking together iii gases emerge from the ceramic body and the glaze itself during firing l the gases mostly contain air water vapor and carbon dioxide 2 the gases are in the form of bubbles which rise to the surface through the glaze and quotpopquot or break 3 after the bubbles break the surface smoothes out 4 bubbles can become trapped in the glaze a if the glaze is too viscous not uid enough b if gases continue to be released during the firing process c if the firing time is too short 3 Glaze composition W999 network former silica SiOz intermediate alumina A1203 network modifier ux K20 CaO NazO PbO colorants opacifiers bubbles etc composition is related to viscosity ow at firing temperature composition is related to expansioncontraction of glaze upon heatingcooling 4 Glaze fit a As mentioned above the glaze composition in uences the amount that the glaze contracts upon cooling dimension changedegree of temperature thermal expansion coefficient Hence it is important that the composition of a glaze be such that it has similar thermal contraction as the ceramic body If not i crazing glaze contracts more than ceramic body as the body contracts the glaze is forced to quotstretch outquot and cracks Crazing Shivering ii shivering glaze contracts less than the ceramic body as the body contracts the glaze experiences compressive stresses and rises off the body while cracking 5 Glaze structure a underglaze i used to coat the ceramic body to provide a uniform surface and a different color ii opaque white underglaze was used as a background for color decoration as in maiolicamajolica overglaze i colored overglaze enamels to add decoration usually on a white ceramic body especially on porcelain ii transparent overglazes to provide glossy surface as in maiolicamaj olica 6 Optical effects in glazes a Color effects are achieved in a similar manner as in glasses see review on glass i colloidal metals ii dissolved metal oxide colorants iii opacifying crystals tin oxide SnOz for example Interaction of light with material in glaze i Bubbles and quartz grains in Celadon porcelain about 01 mm in size and thus at the limit of resolution by the unaided human eye This makes them interesting to the eye They add internal re ections that increase the brilliance of the glaze ii Crystals anorthite and wollastonite crystals in Celadon glazes ware are a bit smaller than a micrometer about 05 pm copper and silver particles in Islamic lusterware are about 400 A in diameter These particles are thus on the same order of magnitude as the wavelength of visible light and can scatter light iii Emulsion of two different liquids in Jun ware produces droplets that are about 800 A or 08 pm in diameter These are able to scatter light since the wavelength of visible light is between 400 and 700 A and thus has the same order of magnitude Interaction of light with glaze surfaces i If the surface of the glaze is completely smooth then light is re ected in a specular manner and the surface appears shiny and glossy ii If the surface of the glaze is rough 7 as a consequence of crazing shivering perhaps 7 then light is re ected in a diffuse manner and the surface appears matte l crazing of the glaze is often intentionally used to create a decorative effect 7 Renaissance Majolica from Italy a red porous gray body bisque unglazed body after ring b white opaque ground or underglaze bianco i 0305mm thick ii crushed quartz sand and crushed feldspar a rock that contains potassium oxide aluminum oxide and silica iii lead oxide iv tin oxide SnOz opaci er c thin pigment layer 005 mm thick i some pigments that don t dissolve in glass the glaze and do not ow while ring this allows the painting of good outlines and precise gures 1 red yellow orange white black are insoluble prepared by fritting or reacting the ingredients in a solid state by heating so that they form compounds insoluble in glass ii blue and green colors are produced by colorants dissolved in glaze d coperta coating transparent overglaze that smoothens surface and provides specular re ection as well as some protection against abrasion of colors i 002005 mm thick ii wets the irregular surface produced by the pigment particles iii contains lead silicate which was produced by heating lead oxide together with crushed quartz sand fritting then grinding the frit to a ne powder which was sprinkled on the surface of the pigment layer e All three layers red together in a single operation without the danger of pieces sticking together
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