Thursday, August 02, 2012

Nitrocellulose, not Acetate!

Every Tuesday night I digitize another home recording disc from my collection. I have ripped over 100 and will probably break 150 before I exhaust my current sources. I refer to them collectively as "transcription discs" which confuses some people. I'll get into why in a second, first an important definition.
Tran·scribe (trn-skrb)
tr.v. tran·scribed, tran·scrib·ing, tran·scribes, tran·scrip·tion
1. Text. To make a full written or typewritten copy (dictated material, for example).
2. Computer Science. To transfer (information) from one recording and storing system to another.
3. Music.
a. To adapt or arrange (a composition) for a voice or instrument other than the original.
b. To translate (a composition) from one notational system to another.
c. To reduce (live or recorded music) to notation.
4. Audio. To record, usually on tape, for broadcast at a later date.
A transcription disc is also called an acetate disc, test acetate, dubplate , lacquer or instantaneous disc.  In collecting circles transcription is meant for commercially mass produced radio recordings intended for distribution. In their lingo a lacquer is probably the most accurate for the home recordings I digitize, though that's also often meant to refer to a high end master recording. The term instantaneous disc sort of covers the shoddy make and disposability of the discs but even some of the supposedly good quality discs can fall apart. I've come to believe that transcription should be adopted as the correct term for them all as a group. Just look at the dictionary definition!

The most common term is "acetate disc", and it is the most incorrect term of all. It dates to before 1934 when such discs were coated in what was sometimes inaccurately called "wax" but was usually ethyl cellulose or cellulose acetate. The coated disc is not exactly original. Edisons first cylinders in 1877 were tinfoil wrapped around a small metal cylinder. In 1885 Chichester Bell and Charles S. Tainter developed a cardboard cylinder coated in a compound of Beeswax and paraffin. [source]

None of these post-1934 discs contain a drop of acetate. Acetate is any derivative of acetic acid. it's most common form is cellulose acetate, which  is used as a film base in photography, cigarette filters and in adhesives. All makes and models of discs are coated in nitrocellulose, not acetate. Nitrocellulose lacquer is made by taking cotton and treating it with sulfuric and nitric acid, which makes an acidic pulp. This can be strained to produce a thin watery resin. It's treated with a strong base to eliminate the acid like potassium hydroxide or sodium bicarbonate. Then the remaining resin can be mixed with a solvent, like acetone and plasticized (at least early on) with Castor Oil producing the "lacquer" that coats transcription discs.

Nitrocellulose lacquer was first invented in 1921 by Edmund Flaherty using the above process. He worked for the DuPont Chemical Company. DuPont sold the rights to Ford. Ford had found that it could be mixed with pigments thus making a quick-drying paint. Ford was all about a faster cheaper assembly line. The leap from painting it on sheet metal car chassis to metal core discs wasn't huge. It is also used as a wood finish, in laquerware, and gun cotton.  His work was derived from that of Henri Braconnot who discovered in 1832 that nitric acid, when combined with starch or wood fibers, produced a combustible explosive material that he called "xyloïdine." In 1838 Théophile-Jules Pelouzediscovered it again experimenting with acid treated paper. He called it "nitramidine." A third chemist, Professor F. J. Otto discovered it again in 1846, and he was the first to publish the process. More memorable was it's discovery by Christian Friedrich Schönbein. He discovered the process after he accidentally detonated his cotton apron. You can't top that.If you want to read more abotu the very early developments of nitrocellulose you can dig up the 1911 book Nitrocellulose industry: a compendium of the history, chemistry Vol 1 &2 by Edward Chauncey Worden.