IMPREGNATION OF ROUGH TO DISGUISE DEFECTS
Knowing that cracks detract from the value of rough, some overseas dealers in large parcels of rough, notably Brazilian and Indian dealers, sometimes practice a deception which the buyer should guard against.

They soak the rough in an odorless and colorless vegetable oil, which has two “improving” effects: (a) it heightens the color, and (b) it fills small cracks and pores, lending the impression that sound material is being bought. While the use of oil for revealing true color has some justification—in fact, many materials offered for sale these days are cus¬tomarily immersed in water for this purpose—the buyer must remember that small cracks, pores, and soft spots are also disguised by immersion and keen disappointments can occur after lapidary work begins. To be safe, it is wise to take a typical sample from a parcel of treated rough, .wash it in soap and hot water, and then dry it off until all traces of water have disappeared. The sample will now appear in its natural state 2nd the buyer will know what he is getting.

SAWED BLOCKS AND SLABS
The great advantage of sawed blocks and slabs is that much guesswork as to quality is removed. The fresh, flat surfaces provide clear indications  of color, pattern, texture, and presence or absence of defects. Another advantage is that sawed material is usually sounder because the mere act  of sawing causes faulty rough to fall apart along the cracks created by natural forces or the hammer blows of the miner. This is an important consideration to the carver seeking good material.
Thin slices or slabs are sold in quantity to cabochon cutters. They should be about 3/16″ thick for ordinary cabochons, or perhaps some¬what thinner for small stones, and a little thicker for larger stones. Slabs that are much thinner or thicker are merely wasteful unless cut to order for some special project. Crudely cut slabs should be avoided; these can be recognized by pronounced grooves left upon their surfaces by an im¬properly operating saw. Particularly to be avoided are slabs with soft spots; these can be detected by merely wiping the surface with a wet cloth and noting if any places appear to dry much more quickly than the remainder of the slab; such places are probably porous and will re¬fuse to take a polish. All sawed pieces and slabs cost more than mine-run rough because of labor and wear and tear on sawing equipment. A num¬ber of lapidary supply houses in the United States undertake custom sawing, charging at the rate of from five cents to fifteen cents per square inch, depending on the volume of work and the type of material. Costs rise sharply if the rough consists of small nodules which are particularly : toublesome to handle and require much attention during sawing.