1920 Rock Records

[Craig Maier]

Did you know that the Edison Lateral Cut records were "Rock Records". Well, they were made predominently of 200-mesh epidote {crushed rock - Ca2(Al,Fe)3Si3O12OH)}. We were given this information by Leah S. Burt, a museum curator at the Edison National Historic Site when we were working on the Edison Laterals transfer project. Leah is a chemist and provided the information so that we would have a better understanding of how to handle the collection.

I suspect that all Shellac 78 RPM records used a similar chemical formulation. The crushed rock was probably there to keep the steel needle sharpened as the records played. I also suspect that the ground-up rock accounts for a lot of the "hiss" that we hear on old 78's.

The entire chemical formula for Edison 78 RPM Needle or Lateral-Cut records is as follows:

1.25 g. gas black
1.5 g. cotton flock
30.75 g. 200-mesh epidote
5.5 g. orange shellac
11.0 g. garnet shellac

[DJBohn]

You had me going for a second there Craig - just had to read your thread! The first thing I thought to myself was "WHAT??? Rock & Roll in the era of Fox Trots???" Anyway...

I wonder if Edison got any of the crushed rock from Minnesota. (not sure what the "epidote" consists of) St. Cloud, MN is considered around the state as "The Granite City". In the nearby town of Cold Spring (yes, where Cold Spring Beer comes from), the Cold Spring Granite Company has been operating since I believe the mid 1800's & they shipped by rail all over the country.

[Ringmaster]

I read a lot of technical material, but retain very little of it; however, I did read that there was an additative to the 78 RPM record base compozition? (spelling), that did indeed serve to help sharpen the needle (seems like it was carbon black), but I am not sure what the base material was ( I think it was shellac).

Just sharing some trivial information

[Craig Maier]

I am not sure since I am not a chemist, but I think that the carbon black just gives the record its color. The two varieties of shellac are probably the binder and the ground rock is the principal ingredient that the record is made out of. The ground up rock particles are probably held together with the shellac(s) acting as the glue. Lastly, the cotton flock probably improves the sheer strength of the disc making it a little less brittle.

[Doug]

less brittle? lol...I guess that's one idea of Edisons that didn't really work.

My understanding is that shellac never really hardens - it's a soft finish, making it a good binder for records (or polish for woodwork). Maybe the cotton is just a filler to lighten the record weight insetead of having a heavy metal base???

[Craig Maier]

Yeah, 78's are pretty darn brittle no matter what they did to try to strengthen them. I noticed here in a technical article by Leah S. Burt that the real thick 80 RPM Diamond Discs used a completely different formulation which did not involve the use of any Shellac. Those records are so thick that you could probably use them as a frisbie-like weapon and then play them just fine thereafter. They look indestructable.

[Doug]

you could probably use them as a frisbie-like weapon

Unfortunately...being young..been there & done that! Those normal shellac records are deadly when thrown - a good self defence for intruders!

Imagine the press "Old man decapitates intruder with vintage record collection"
I'm not sure if that would really happen, but after what I've seen they can do, I'm not game enough to throw one for our dog.

[DJBohn]

Craig, I've got a handful of those 80 RPM Diamond Discs. They're about a 1/4" thick, but not as indestructable as you might think, as a few of them have some chipping around the edges. Others I have though, look as if they have never been played as there is no visable wear. They are just as shiny & reflective in the sunlight as you would expect from a new vinyl LP! I could send you a list of what I have if you're curious...

[Craig Maier]

I know that they can de-laminate. That is because the inner core is made with a different process than the outer recording surface layer which is ulike standard 78 RPM lateral discs. It is particularly important not to allow a Diamond Disc to become wet or damp because of this construction.

Thanks for the offer to catalog your Diamond Discs, but we have quite a pile of them here - - - about 70 of them. Never play them on an old Victrola which will ruin them. They must be played on an Edison Diamond Disc phonograph or on a modern sterephonic turntable.