About
Celluloid originally referred to products made from cellulose nitrate but now is used to refer to similar, more stable chemical compositions of plastics. It was one of the first industrial thermoplastics and revolutionized the world when it became widely produced. Originally designed to provide a cheaper alternative to ivory but later was used for film and a variety of purposes including imitating other expensive materials. It eventually fell out of favor due to its extreme flammability and dimensional instability which caused it to shrink and distort with age. It still remains a staple of the guitar world due to its widespread usage in vintage instruments and the community's desire to use and repair with authentic materials.
Tortoise shell imitations were one of the more common materials used in old instruments for pickguards and appointments and they varied wildly in design and color. Many modern tortoise shell imitations are simply printed designs on opaque or transparent plastic which is often unsatisfactory for restoration work and can look cheap. Proper imitation tortoise where colors are added to a transparent sheet can still be purchased and can even be purchased in cellulose nitrate but they can cost more and cellulose nitrate usually requires a hazmat fee to ship.
The art of making quality imitation tortoise was likely passed from worker to worker in these factories and has likely been lost to the ages but people have relearned the process and continue to make pretty darn good replicas. The purpose of this research is to document the historical processes that were used and what chemicals were involved.
The Process
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| [1] The first method comes from a 1907 book by Friedrich Böckmann entitled "Celluloid" which discussed the process of creating, working, coloring, and uses for the material. It is the book to read if you are interested in making celluloid but I highly recommend not doing so unless you have a concrete bunker far away from anything valuable. Most of the celluloid factories have burned down, if that's any indication. I've included an excerpt which discusses the process of creating imitation tortoise shell with celluloid. They first produce a sheet of clear, polished celluloid and dye it yellow with a solution of picric acid and a aniline brown. The exact parts unknowns. Then red spots are added via another solution of aniline brown and fuschin dye. |
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Finally the article mentions the "very best of all methods" which involves hand coloring individual sheets which results in a product that is "almost impossible to distinguish" from the real thing. It doesn't elaborate any further.
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An excerpt from "Workshop Receipts: For Manufacturers and Scientific Amateurs, Volume 4" written in 1917 describes the celluloid imitation tortoiseshell. It first involves taking celluloid in a paste medium and mixing a part with brown aniline dye, mixing another part with yellow dye, and kneading them into a part of clear celluloid.
Sources
[1] Celluloid by Friedrich Böckmann: https://books.google.com/books?id=2ok6AAAAMAAJ
[2] Textile Colorist and Converter Vol. 44: https://books.google.com/books?id=5qs7AQAAMAAJ
[3] Cellulose, Cellulose Products, and Artificial Rubber by Josef Bersch: https://books.google.com/books?id=pe5QAAAAYAAJ
[4] Workshop Receipts: For Manufacturers and Scientific Amateurs, Volume 4: https://books.google.com/books?id=cs9MAAAAYAAJ
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