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igneousone of the three great classes of rock (igneous, sedimentary, and metamorphic), solidified from molten slate, as granite and lavas.
ilmenitea mineral having the theoretical composition fe0 ti 02 used principally in the production of titanium oxide. 
imperviousthat degree of vitrification evidenced visually by complete resistance to dye penetration.note: the term impervious generally signifies zero absorption, except for floor and wall tile which are considered .,impervious’up to 0.5 per cent water absorption.
impervious tilehas water absorption of 0.5 percent or less.
impregnationapplying a chemichal containing stain inhibitors that penetrates below the surface of the stone.
inciseto cut inwardly or engrave, as in an inscription.
inciseddecorated by cutting or indenting the ware surface. 
inglaze decorationsee decoration, inglaze.
initial setting timethe time required for a freshly mixed cement paste, mortar or concrete to achieve initial set. (see also final setting time.)
inscriptionlettering cut in stone.
isolation jointa separation between adjoining parts of a concrete structure, usually a vertical plane, at a designed location such as to interfere least with performance of the structure, yet such as to allow relative movement and avoid formation of cracks elsewhere in the concrete and through which all or part of the bonded reinforcement is interrupted. (see also contraction joint.)