---- ----, improving, 178 ---- ---- colours, 176–184 ---- ----, trade names of, 201 ---- earths, 5 Grey earth colours, trade names of, 202 Grey earths, 38 Gypsum, 18, 19, 111, 112 Heavy spar. _See_ Barytes. Hematite, 155 ----, brown, 23, 30, 31 ----, red, 28, 30 Hydro-extractor, 66–70 Improving earth colours, 84, 85 Indian red, 29, 160 Iron cream, 29 ---- glance, 154 ---- in limestone, 17 ---- ore, bog, 25, 31 ---- ----, micaceous, 28 Ironstone, brown, 23, 24, 25 ----, clay, 24 ----, red, 28–30 Kaolin, 21, 22, 112–119 Lazulite, 183 Lemnos earth. _See_ Bole. Levigation, 60–65 Lime, absorption of carbon dioxide by, 93 ----, action of, on casein, 94 ----, ----, on colours, 93, 98 ----, calcining, 88–90 ----, caustic, preparation of, 87–94 ----, double compound of oxide and carbonate, 93 ---- from mussel shells, 98 ----, impurities in, 91, 92 ---- in clay, 22 ---- ----, eliminating, 117–119 ---- in ochre, 129 Lime in the preparation of artificial ochre, 140–144 ----, moulding, 96–98 ----, quick, 16 ----, slaked, 16 Limestone, 11–18 ----, suitability of, for colour-making, 92 Limonite, 25 Magnesia, carbonate of, 123, 124 ---- in lime, 91 ---- in limestone, 17 Magnesium silicate, 21 Malachite, 35 ---- blue, 183 Marble, 11, 14, 15 Minerals, testing for suitability as pigments, 172 Mine sludge, 32 Mixing earth colours, 81–84 Moulding, 85, 86 Mountain chalk, 12 ---- milk, 12 Muffle, burning ochre in the, 158–160 Muriacite, 19 Muschelkalk, 13 Ochre, 24, 25, 26 ----, blue. _See_ Vivianite. ----, calcining, 132–136 ----, English, 138 ----, green, 180 ----, pit, 148–150 ----, Roman, 137, 138 ----, Siena, 137, 138 ----, testing, 130–132 ----, toning with chalk, 144 ----, toning with clay, 144 ----, vitriol, 146–148 Ochres, 128–150 ----, artificial, 138–146 ---- as by-products, 146–150 ----, burnt, 158–164 ---- from various deposits, 136–138 ----, Italian, 137, 138 Oolithic limestone, 13 Organic matter in lime, 91 Pastel crayons, 126 Pearl white, 94 Permanent white, 19, 122 Pipeclay. _See_ Kaolin. Preparation of colour earths, 40–86 Pulverisers, 56–58 Raddle, 29, 155–158 ----, impurities in, 156 ----, testing, 157 Raw materials for earth colours, 8–39 Red earth colours, 151–167 ---- ----, trade names of, 200 Red earths, 4, 27–33 Sampling raw earths, 9 Selenite, 18 Shading pigments with permanent white, 19 Siena, Terra di, 25, 26, 27, 168–170 ----, ----. _See also_ Italian ochre. Siderosilicate, 171 Sifting, 77–80 Soapstone, 20, 21. _See_ also Steatite. Spanish brown, 174 Sprudelstein, 15 Steatite, 20, 21, 125, 126 Stamps, 45–48 Talc, 20, 21, 124, 125 Terra sigillata. _See_ Bole. Testing purity of raw earths, 10