Stone
For tumbling of rocks as a lapidary technique, a plastic or rubber-lined barrel is loaded with a consignment of rocks, all of similar or the same hardness, some abrasive grit, and a liquid lubricant. Silicon carbide grit is commonly used, and water is a universal lubricant. The barrel is then placed upon slowly rotating rails so that it rotates. The optimal speed of rotation depends on the size of the tumbler barrel and materials involved.
A well-chosen speed for stone polishing causes the rocks within the barrel to slide past each other, with the abrasive grit between them. The result of this depends on the coarseness of the abrasive, and the duration of the tumble.
Typically, a full tumble polish from rough rock to polish takes between 3–5 weeks, and is done in a minimum of 3 steps. Initially, the rocks are smoothed with a coarse grit (such as 60-90 mesh). This is followed by washing and then a stage of finer grits (120-220 then 400-600 mesh), before the (optional) use of a pre-polishing compound (1200 grit), a washing cycle with detergent to remove any grit on the stones. The final step is a polishing stage using powdered polish, (such as cerium oxide or tin oxide), water, and often small plastic pellets that are designed to cushion the stones as they tumble (so as not to cause chipping) and carry the polish evenly across the stones. The precise tumbling time is determined by many factors, including the hardness of the rock and the degree of smoothing desired in the coarser steps. Some people will tumble stones with rough grit for two, three or even four weeks to get their desired shapes out of the stones.
Sometimes, stone "preforms" are used. This refers to cutting shapes from the rough rock, before tumbling. This gives more control over the final piece, so shapes such as a tear drop can be produced. The technique is still limited to rounded shapes. Preforms may use less time with the coarsest step, or skip it altogether.
During the 1970s, small rock tumblers were a common hobby item, and jewelry decorated with tumbled semi-precious stones was very much in fashion. Likewise, dishes and decorative glass jars filled with tumbled stones (often including common rocks not suitable even for costume jewelry) were frequently used as household ornaments.
Read more about this topic: Tumble Finishing
Famous quotes containing the word stone:
“I passed a tomb among green shades
Where seven anemones with down-dropped heads
Wept tears of dew upon the stone beneath.”
—Unknown. The Thousand and One Nights.
AWP. Anthology of World Poetry, An. Mark Van Doren, ed. (Rev. and enl. Ed., 1936)
“You see, in a world where elephants are pursued by flying men, people are just naturally going to want to get high.”
—Judith Rascoe, U.S. screenwriter, Robert Stone (b. 1939)
“The finest workers in stone are not copper or steel tools, but the gentle touches of air and water working at their leisure with a liberal allowance of time.”
—Henry David Thoreau (1817–1862)