In his book titled "Rare Smoke - The Ultimate Guide to Pipe Collecting" Richard Carleton Hacker had this to say, in part, of the Dunhill Shell finish:
"Alfred Dunhill patented the sandblast in 1917 (Patent No. 1484/17) although some early company brochures state that the Shell was accidentally discovered in 1914. Interestingly, records indicate that the finish was actually being produced as early as 1912, the same year the white spot was introduced. The finish was made possible when the Masons Yard factory acquired a gas stoving machine (initially consisting of a gas furnace, asbestos sheeting and some old piano parts) for treating the raw briar bowls that were being brought in from France. The intensity of the steam and heat was so great, some of the softer wood was actually etched or shrunk away from the harder outer surface of the bowls."
According to the aforementioned John C. Loring, in his patent application Mr. Dunhill explained his invention, in part, as follows:
"This invention relates to the treatment of the surface of the wood in wooden tobacco pipes, for decorative purposes, and refers to a process by which the grain is accentuated or made to stand out in relief, thus giving the wood a very elegant appearance, without interfering with the durability of smoking qualities of the pipes."
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"Although the sand blast has been used previously for the treatment of the surface of wood, to accentuate the grain, I have found in practice that this treatment in itself does not give satisfactory results as there is a tendency for the wood to become cracked and injured, a result that does not occur with my process where it is used as an auxiliary to the treatment by steeping (in oil) and by heat."
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"In carrying out my invention, I shape the pipe in the ordinary way...I then steep it for a suitable time in mineral or vegetable oil. For instance, in the case of Algerian briar, a wood very suitable for the production of these new tobacco pipes, the article may be steeped for a long period say for several weeks, in olive oil.
"After it has been removed from the oil, I subject the article to the action of heat...This process occupies a number of days, the oil exuded or coming to the surface being wiped off periodically. The result of the treatment is that the grain of the wood is hardened and stands out in relief to a certain degree, but the oil coming to the surface forms an impervious coating."
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"I (then) submit it to the action of the sand jet or sand blast, which removes the hardened coating of oil and also has the effect of cutting away the softer wood between the grain and leaving the harder portion-the hardness of which has been intensified by the process of steeping and heating-in very high relief.
"If the article is again steeped in oil, it will take up a further amount...and the treatment by heat and the sand jet or sand blast may be repeated; and so on for as many times as may be required according to the extend to which it is desired to accentuate the grain or make it stand out in relief.
"The resulting article is extremely hard and constitutes an admirable tobacco pipe for the smoker."