GLAZING EARTHENWARE AND PORCELAIN. In the bisquet state, earthenware and porcelain will adhere to the tongue, and imbibe moisture. The tendency of the earths to absorb water is the cause ; and the ware in this state would not retain water and many other liquids. Hence, there is necessity for an artificial vitrified covering, whose com ponents are so adapted to those of the body as to be equally affected with them by change of temperature, and preserve equality of expansion or contraction.
We have not yet discovered a body and glaze that will be complete ware by once baking. The components of the present bodies do not sufficiently con glomerate to remain unaffected by the moisture of the glaze, but the articles become soft, and either shrink, or alter their figure. The only probable sugges tion towards this is :—Grind very well some of the flesh-colored feldspar from Montgomeryshire, precipitate whatever iron may be in the mineral, then add 8 per cent. of ground native carbonate of barytes, and 1 per cent. of cobalt blue calx ; mix in water for dip and glaze, and fire only once. Feldspar is the glaze of Nankin porcelain.
The manufacturers have their particu lar glazes, for certain bodies. The several components are carefully proportioned, then ground to a pulpy state, almost im palpable between the thumb and finger ; this is mixed with a certain quantity of water, and kept agitated to preserve uni form suspension. The dipper places nigh him a board covered with bisquet ware, and another with a number of small pegs or nails. lie immerses (or dips) each article, with a suitable motion to cover the whole, then places it on the pegs to drain. The water is imbibed by the pores of the ware, and, to the thick ness of writing paper, the components form a covering, which is vitrified by baking. From the pegs the vessel is placed in a nagger, and at a lower heat of the oven the whole glaze is fused.
The following are excellent glazes : Fos PORCELAIN.—Pulverize well, and carefully fuse together, flint 20 parts, Gullet 7, Cornish-stone 20, red lead 20, borax 20, subcarbonate of soda 7, nitrate of potash 8, oxide of tin 21, cobalt ealx 1. Or, Fuse together, flint glass 66 parts, red lead 15, arsenic 7, muriate of soda 5, ni trate of potash 6, cobalt calx 1. When well ground, mix with Cornish-stone 40 parts, frit (as above) 18 parts, flint 12 parts, and white lead 80; grind in the glaze mill, and use carefully.
Fuse together Cornish-stone 80 parts, soda 20; piulverize, and grind together, for use. The fritt 40 parts, flint 16, Cor nish stone 24, end white lead 20.
Fuse together, cullet 85 parts, flint 10, white lead 2, arsenic 1, nitrate of potash 2; then grind together, fritt 80 parts, Cornish - stone 40, flint 25, boracic acid 5.
The feldspar glazes are subjoined for general purposes of utility. They are most secretly preserved by their first em ployers, but it is well they be exten sively known.
Fuse together, feldspar 66 parts, borate of soda 34; then grind, and mix with flint 95, nitrate of potash 5, ground for use.
Or, feldspar 60, borax 40, fused, and mixed with flint 50, potash 2.
Or, feldspar 90, carb. barytes 7, lime 2, magnesia 1 ; and mixed with flint 67, borax 30, and potash 3.
Or, feldspar 60, borax 24, nitro 6, salt 4, and potash 6, mixed with flint 60. Raw glazes.-White lead 45, Cornish stone 22, cullet 22, flint 8, borax 2, salt 1'. Or, white lead 51, Cornish-stone 25, cullet 11, flint 12, earb. potash 1.
hite lead 49, Cornish-stone 24, cutlet 10, flint 14, borax 3.
Or, white lead 42, Cornish-stone 27, cutlet 14, flint 11, bor. acid 6.