The successful user of roughstuff is one who duly considers the importance of having a correctly-proportioned, finely-balanced mixture skillfully applied to the surface amid surroundings favorable to its prompt and thorough drying.
A guide coat to be used over roughstuff is made of a little of the 'stuff colored a bit with yellow ochre or Venetian red and thinned down considerably thinner than the 'stuff, with turpentine.
The workman who has roughstuff to rub requires, as an outfit, plenty of clean water right at hand, a good sponge, chamois skin, and a varied assortment of rubbing stones and bricks. The rubbing brick product, of German origin, has been considerably improved of late years; to such an extent, in fact, that it is now possible to obtain it as fine as wished for, and running from that up to a very coarse quality. However, for the very high class work, the natural lava, or pumice stone, is not to be surpassed. The quality of the rubbing accomplished depends much upon the selection of the blocks of pumice stone. The blocks of light weight, open grain, tunneled with innumerable air cells, are to be preferred for good cutting properties. Immersed in water, they float instead of sinking. The buoyancy of a piece of lava determines its porosity and its cutting power. This kind of stone may be used until the surface is well reduced, when, preferably, the stone of closer texture and tighter grain may next be used and continued in use until the final dressing up has been concluded. Select stones of large cutting surface. After the sawing, filing, and necessary dressing up of the stone in preparing it for the surface, it merits a thorough washing and rinsing to cleanse it from all minute atoms of grit, etc. In the actual work of rubbing a surface, keep the surface well washed to prevent gumming of the stone and to enable the eye to see just what the mind and muscle are doing; but do not flood the work with water. The rubbing stone is doing its work properly when, under an even, gentle pressure, it cuts smooth and free with a clinging, adhesive motion. When a particle of grit becomes lodged under the stone there will be a rolling, jarring motion, easy for even an unpracticed hand to detect, provided vigilant attention is being directed upon the work. When scratching of the surface occurs, the rubbing stone requires smoothing off with another stone, and the surface, stone, etc., given a thorough rinsing with clean water. Circular, zig-zagging motions of the stone are ill-advised. Straight, clean strokes, all directed in one general direction, are best and most effective. A surface is not always rubbed sufficiently fine when the guide coat disappears. The guide coat may be but a mere wash and disappear almost completely under a few strokes of the stone. The disappearance of such a guide(?) coat is not evidence that the proper surface has been reached. By repeatedly drawing the hand, with a good pressure, across the surface at right angles with the direction that governed the laying off of the final coat of filler, the workman can very accurately decide when an adequately fine surface has been reached.
To determine when a surface has been rubbed just enough usually gives the inexperienced rubber no little difficulty, but with practice he will master the accomplishment. On moulded panels it is advisable to rub the edges of the surface first, as it will lessen the tendency to thrust the stone forcibly against the moulding, thus chipping off atoms of stone to be ground into the surface later on.
Rubbing the roughstuff is the final process in the art of developing the comely and durable foundation. Does not the work, then, merit a full measure of skill, alertness, and patience in its execution?