As for the carbon black and other minerals, something similar had always been added to disc composition. The principle had always been that cheap steel needles, which could not be individually ground to precise shape, were used. The needle was intended to be ground to the shape of the groove by the groove itself, in the first few revolutions, which is why it is ofter the first few grooves which are most worn. For this reason, as well as to withstand the huge pressure of the playing weight on a needle point, the material had to be hard and abrasive. The up till then usual binder is given in the patent as shellac, but I believe that even then standard materials used a mixture of resins of which shellc might not have been the main one.
The "Process" of course was supposed to eliminate surface noise by using a very fine material. The record was laminated - a blank was pressed in coarse material, and the fine material was coated onto fine paper. Two sheets of the fine material were put in the press, with the coarse material between, and the final pressing formed a thin surface in the fine material on top. Columbia had been laminating their records by this process since about 1907, and often their surfaces before 1923 are very good, because although they used conventional materials they could afford to use a better composition as it was only needed in small quantities.
In laminating they were far from unique.In fact, the Bell-Tainter Graphophone, the original Columbia talking machine, used a wax-covered paper cylinder. Polyphon had issued discs of wax on metal about 1901, and before 1905 Nicole had used rubber on cardboard, Neophone had used celluloid on cardboard and Pathe wax on cement! In 1906 U.S. Columbia (American Graphophone Company) had patented a celluloid-shellac composition on cardboard. This may have been for the unsuccessful Marconi Velvet-Tone records they produced. In 1907 they patented their laminated disc process, and this was used from about that time.
In 1911 British Columbia patented the change from thick to thin paper for the support for the playing surface when first made. The thick paper apparently caused problems, and could tear in pressing. It seems possible that the 'rivulets' seen in most laminated Columbias up to 1923 is due to deliberately allowing the paper to tear in the press, harmlessly except for the appearance. Alternatively it is simply due to the flow of the material in the press. I can't explain why these rivulets are never seen in New Process records - possibly the properties of the new surface composition got rid of the problem.
No doubt Edison's Diamond Discs from 1913 were the impetus for developing fine surfaces. Edison used a synthetic material laminated onto a coarse base, and his material was very hard fairly noiseless in spite of the low recording levels on Diamond Discs. There is some low to mid-frequency noise, due to the slight 'waviness' of the surface unavoidable with laminated discs. This is present on Columbias as well but is only noticeable on Diamond Discs because of their vertical cut and low recording level.
One other way in which UK Columbia tried for silent surfaces is in heavily buffing the masters. In pre-1923 issues, the surface outside and just inside the recorded grooves always showed fine grooving as if the cutting needle had been tracking across but with no weight on it, but actually possibly caused by a sapphire 'advance ball' which helped control the cutter head. In post-1923 pressings these are buffed out completely from the outer margin and the whole playing surface shows signs of buffing. I believe this buffing has an insidious effect on the sound as well, and often a pre-1923 copy will sound much brighter, especially if it's one with a fine surface.
The other thing that shows the store UK Columbia set by New Process is that the label was completely changed at exactly the same time as it came in. Pre-NP's had 'COLUMBIA RECORD' round the label edge, and NPs had the familiar 'Columbia' in a straight line. The only exceptions were the few McCormack repressings from Odeon, which have the NP label but are not on NP material. Maybe they were pressed for Columbia by somebody else.
The label change seems to have been similar with US Columbia.
In the UK Columbia used New Process until the 1931 merger with HMV, Parlophone, etc. as EMI.
Doesn't actually answer David's question, but hopefully of some interest!