Identifier: annualreportof5421900newy (find matches)
Title: Annual report of the Regents
Year: 1889 (1880s)
Authors: New York State Museum University of the State of New York. Board of Regents
Subjects: New York State Museum Science
Publisher: Albany : J.B. Lyon, State Printer
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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h the ex-pansion of the imprisoned air. When properly pressed, this doesnot happen. It is highly essential that the composition of the body shouldbe such that the ware will both dry and bum without cracking orwarping. The temperature attained in the burning of these tiledepends naturally on the nature of the clay, but it often reaches thfemelting point of feldspar, as this material is used to a large extentto aid in the vitrification of the body. Tiles are open to the same trouble from efilorescence, due to thepresence of soluble salts in the clay, as other clay products, and thetrouble has to be corrected in the customary manner with barium. Another method of preventing the formation of these coatingson the surface, is to coat the face of the tile with petroleum or tarso that the evaporation in drying can take place only from the backof the tile. (Langenbecks Chemistry of pottery, p. 154) In thefiring, this coating of oil or other material burns off, without having I-I- ciO H ^ 0) 0^
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&£ Cp. T. O CLAYS OF NEW YOKK 775 done any harm. The soluble salts may also get into the clay fromsome of the materials used to color the tile artificially, umber, forexample, being seldom free from sulfate of lime. Floor tile should be burned to a condition of great density, inorder that they may not absorb water, nor permit the entrance ofdirt into their pores, rendering their cleaning more difficult. Langenbeck (Chemistry of pottery, p. 156) gives the followingpercentages of water absorbed by floor tile of different colors. Water absorption of floor tile Color of the clay Extremes Averages Salmon 1.5—9.1 5.8 Buff 1.9— 7.2 4.6 Light gray 1.9—8.5 5.8 Darkgray 2.0— 5.8 4.4 Chocolate 0.0— 7.4 4.8 Eed 1.5— 8.4 6.0 Black 4.4 — 10.3 7.5 Fawn 8.3 In the manufacture of encaustic tile, the clay that is to form thesurface of the tile and give the pattern is charged into the moldfirst, while the clay that makes up the body is then put in on topand the whole subjected to pres

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