When grinding red pastes for use as base for dipping wood or metal it is not practical to assume that any ordinary oxide of iron red will be good enough for the purpose. The chief points in the property or characteristic of such base are that it must hold well in suspension when thinned for use with the volatile liquids usually employed for the purpose; that the pigment when settling or standing about for a time must not cake hard or be gummy in the bottom of container; must be so as to readily reincorporate with the thinners and must cover well the objects on dipping when the paint is made thin enough to drip freely. To attain this end it is by far the best policy not to select red oxide or Venetian red low in cost, but to disregard cheapness in first cost and select grades that are high in percentage of sesquioxide of iron and add a base of light specific gravity to furnish the buoyancy for keeping the paint well in suspension. To enable the grinder to determine the proper kind of inert base he should know for what particular purpose the dipping paint is to be used. For instance, when used for sheet metal or tin, the less inert base is mixed with the iron oxide the better the paint will drip and cover the metal, while for dipping cast-iron parts a base with a good filler is desirable, and the same applies to the dipping of articles of open-grained wood, such as is used for agricultural implements and on cheap wagon work. For example, if a red dipping paint of the type of Venetian red is desired, select a red oxide containing as nearly as possible to 90 per cent of sesquioxide, grinding it very fine in boiled linseed oil to a soft paste, which will require close to seventy pounds pigment and thirty pounds of oil. If ground in this way and thinned with the proper drier and either spirits of turpentine or one of the heavy benzines, known as turpentine substitutes, or ordinary naphtha, as the case may be, the paint should cover well, adhere firmly, leaving only a thin film on the surface that will not sag or run. If a maroon shade be required Indian red or the deep shade of Persian Gulf red can be substituted for the brighter Venetian red type or shade of red oxide. On the other hand, where filling up qualities are desirable an artificial oxide of iron red, containing anywhere from 30 to 40 per cent sesquioxide of iron, with a base of dead burnt calcium sulphate, will supply the filling without any further addition, or a native red of the 90 per cent type mixed with its own weight of fine silica and bolted whiting ground at the rate of 72 per cent by weight of the mixture of pigment and 28 per cent of boiled linseed oil will make a good base for a dipping paint for cast-iron parts or wooden parts of machinery or wagon work. When quick drying is required part of the oil is omitted and a good japan drier used in its place, while the linseed oil should be changed from boiled to raw linseed oil. These bases will answer equally well for gloss and for flat drying dipping paints, the difference being in the thinning of the bases.