The following article, which we extract from "Trade Secrets," contains the pith of the accessible information on this subject: -
A good razor-strop is indispensable, not only to the barber and to those who shave themselves, but to all who require exceedingly sharp cutting tools. The surgeon, the wood-carver, the microscopist, and many other artists, are greatly aided in their work by the use of a good strop.
The basis of the best strop is good hard leather. By hard leather we do not mean leather that has been rendered stiff and hard by alternate wetting and drying, but leather that is so close and firm in texture as to be compressed with difficulty. Leather that is soft yields to the pressure of the edge of the tool, and rises up when this edge passes over it. Instead of a sharp edge, formed by two planes meeting each other, a blunt edge, formed by the meeting of two curved surfaces, is the result, and such an edge can never cut cleanly and well. This arises partly from the defective form, and also from the great increase in the cutting angle of the edge.
Good hard calfskin probably makes the best surface for a strop. Excellent pieces may in general be obtained from the bookbinders for a trifle, and they are easily attached to the wooden holder by means of a little glue. Two surfaces are generally employed: one in its natural condition, and the other after being rubbed with some very hard but fine powder. Of the powders that have been suggested the following give good results: -
2. Emery, brought to a state of the very finest powder by grinding and washing.
3. The charcoal of wheat-straw, or the straw of grasses growing in swamps or marshy places. This charcoal owes its efficacy to the small quantity of silica which it contains.
4. Diatomaceous earth. Of this the famous Tripoli powder is a good example. Such earth is found quite extensively in this country. In its natural state the particles are too coarse, and the earth is apt to be gritty from the presence of fine sand. It should be well ground in a mortar and carefully washed.
5. The fine carbonaceous dust deposited in gas-retorts during the process of making gas. The particles of this black dust are as hard as diamonds, and cut steel rapidly: they are, in fact, very minute diamonds. All these powders ought to be carefully washed, or rather "elutriated," so as to separate the coarser particles and the impalpable dust, which does no good, but, on the contrary, clogs the cutting action of the material. After being carefully washed the powder is dried, and either mixed with a little tallow and wax, or the leather is first rubbed very lightly with the greasy mixture, and then very lightly coated with the powder. When made into cakes with grease the material is known as "razor-paste," and is sold as such. Crocus, in the form of cakes and sticks, can also be found in most tool-stores.
Diamond-dust, or the powder produced by rubbing diamonds against each other in the process of cutting and polishing them, possesses very powerful cutting qualities; and when properly used on suitable "laps" or metal blocks, it enables lis to give a very keen edge to every species of cutlery. Cooley tells us that "the discovery, or assumed discovery, of this fact, a few years since, led certain knaves to extensively advertise and puff a spurious preparation (powdered quartz) under the same of diamond-dust. In a short time the demand for the fictitious article became immense. It soon, however, acquired a bad notoriety. Instead of sharpening cutting instruments it infallibly destroyed their edge, and was particularly unfortunate in converting razors into saws. This discovery was not made until it was in the hands of the majority of the adults in the kingdom; nor before the scamps who had manufactured and vended it had realized a moderate fortune."
It is very evident, however, that the evil effects in this case arose from wrong methods of manufacture and preparation. Quartz crystals,which have been frequently sold as 'diamonds,' under the names of "California diamonds," "Alaska diamonds," etc., were ground as finely as ordinary stamping-mills would grind them: the powder was bolted or sifted, and in this state placed on the market. Now, it is the last degree of pulverization that costs in this case. It is easy to reduce the quartz to coarse powder, and not very difficult to obtain a tolerably fine powder; but to get a quartz powder sufficiently fine and free from coarse particles to serve as a polisher or sharpener for cutlery is a more difficult matter. From experiments we have made it would seem that pulverized quartz might be a very valuable grinding and polishing material; and as it can be had in almost unlimited quantities for nothing, it offers a fine field for enterprise. When thoroughly ground it should be first sifted or bolted, and then washed or elutriated, so as to separate all grit.