But the brand of blank, Tonex is totally unknown to me. The stroboscope on the label makes me think it might have had some kind of audiophile marketing. The manufacturer is listed as "OH &A Selmer Inc. Elkhart, Indiana U.S.A." that I found a little bit about. In a February 1967 issue of billboard I found an article on H&A Selmer Inc. It was a write up for an electric saxophone. They were described as making a wide variety of wind instruments by company president Jack F. Fedderson. In fact Their Bundy model clarinets are said to be among the best selling in the world.
Alexandre was one of 16 siblings, several of which were musicians, most notably Henri-Chery, Charles-Emile and Alexandre-Gabriel. Henri and Alexandre were both clarinetists. By 1890 Henri was a maker of clarinet reeds. In 1895, at the age of 31, Alexandre came to America and performed with a number of orchestras including the Boston Symphony Orchestra, the Cincinnati Symphony Orchestra and the above mentioned the New York Philharmonic. Around 1900 he opened a retail musical instrument store on Third Avenue in Manhattan. It was founded as H&A Selmer Inc. in 1904. If you didn't guess, the H and the A stand for Henri and Alexandre. In 1918 Alexandre returned to France and left the American side of the business in the hands of one of his students, George Bundy. You can read a very detailed biography here that skips acetates entirely.
Their Elkhart plant was built in 1927. In the 1950s they began making brass instruments in addition to woodwinds.They made bassoons, Clarinets, trumpets, oboes, trombones, fluets, and saxophones. They had over 200 different models of just mouth pieces. Benny Goodman played a Selmer. John Coltrane played a Selmer. Coltrane actually played a Mark VI which was assembled in Elkhart, IN. Thsi is all very interesting.. but when did they start making acetates? Well I found an ad in the June 1943 issue of Popular Science that included one crucial detail...
So we know for certain that they were making glass acetates by 1943. It's reasonable to think they were already making standard aluminum core blanks before that, perhaps even in the mid 1930s. By inference I'll assume the Tonex blanks date similarly to the others. it's not certain, but there is enough context to corroborate at least that inference. I do have one lingering question. Why is there an "O" in the company name on the acetate?"Glass recording discs are the latest answer supplied by the phonograph industry to shortages of critical details. The new disks are made on a transparent base of ordinary glass with a coating of slow-burning ethyl acetate. They were developed by H&A Selmer of Elkhart Indiana."

