Records or Disks

Category:Electronic Media
Category:Audio Preservation
Category:Breakage
=History=
The grooved Disk (platter, record) was an invention of Emile Berliner in 1887. Advances over the next 75 years created dozens of sizes (diameters) and colors of Disks, and a variety of rotation speeds (beginning at around 70 rpm) depending on the manufacturer and materials. 
Disks are made through one of two processes. In the master and mother process a recording blank is etched to create the matrix for a permanent mold or stamping for pre-recorded Disks. In the instantaneous process a stylus cuts a groove in a blank Disk to capture original recordings. Disks are usually cut laterally (the groove has side to side impressions), though for a time period in the early 20th century they might be cut vertically (so-called "hill-and-dale" impressions), depending on the manufacturer. 
Disk recordings span the acoustic and electric method of recording. Many Disks, especially instantaneous Disks, are recorded inside-out. 
In general the three eras of Disk materials found in collecting institutions are 
•	shellac type recordings (1897-c.1948) 
•	instantaneous Disks made either of aluminum or cellulose nitrate on a core (cellulose nitrate Disks are also known as acetates and lacquers) (1930s-1940s) 
•	thermoplastic Disks of polyvinyl chloride or polystyrene (LPs and microgroove Disks) (1948-present) 
There are a variety of master recording blank materials as well as unusual Disks developed for specific markets.
=Technical Details=
Chronology, including Material characteristics, Diameters, Rotations:
==Berliner Disk (1887)==
A Matrix recording. Glass covered with lampblack; traced and lacquered; photoengraved. Easily breakable.
==Wax Recording Blank (1888)==
A Matrix recording. Zinc Disk coated with wax; traced; etched with acid
==Berliner Record (1888-1897)==
File:Berliner disc.jpg | Berliner Disk c. 1888
A prerecorded Disk made from a matrix. Hardened latex (latex rubber vulcanized with sulfur) also known as vulcanite; easily malformed.
==Celluloid Disk (circa 1888-1897)==
A prerecorded Disk made from a matrix. Cellulose nitrate; brittle.
==Solid Wax Disk (1896)==
A Matrix recording on solid wax. 
==Shellac Disk (1897-c.1948)==
File:Shellac Recording.jpg | Shellac Disk
A prerecorded Disk made from a matrix. Constituents may be clay (Byritis), powdered shellac, lampblack, cotton fibers (originally known as Durinoid); formulations change from brand to brand, and other resins, plasticizers, hardeners, and fillers may be added. 7 inch, 10 inch, 12 inch, 16 inch. 70 rpm, 78 rpm, 30 rpm. These are fairly stable as long as they are stored in a cool, dry environment.
==Laminated shellac Disk (1906)==
Like the shellac Disk but with a core of heavy cardboard.
==Aluminum Disk (1930s)==
File:Aluminum disk.jpg | Aluminum disk circa 1930]] 
Either a Matrix or instantaneous recording. Aluminum. 12 inches or smaller.
=="Acetates" or Lacquers or "Direct Cut Disks" (1934)==
Either a Matrix or instantaneous recording. Cellulose nitrate lacquer on an aluminum, glass, or zinc core; or cellulose acetate on a core. 10 inch, 12 inch, 13 inch, 16 inch (also unusual sizes larger and smaller) 
This is misnamed as an “acetate” Disk; it is usually cellulose nitrate. Also known as a direct cut Disk it could be used either as a matrix or instantaneous Disk. It may have an aluminum, glass, or zinc core. Typical sizes are 10”, 12”, 13”, and 16”. These have a range of problems from shrinking, peeling, cracking, or embrittlement to an exudation of the plasticizer that leaves a sticky residue on the surface. 
==Dictation Disks (early 1940s)==
Instantaneous recording. These are so-called "plastic" Disks under the names Voicewriter, Gray Manufacturing, Audograph.
==Long Playing (LP) Disk (1948)==
These are prerecorded Disks. Polyvinyl chloride with stabilizers. 10 inch (1948-1960s); 12 inch (1948-present) 33 1/3 rpm
LPs could be produced in “novelty” colors and shapes. LP Jackets or sleeves are often valued for their graphic design. 
==7" Microgroove Disk or "45s" (1948 or 1950)==
These are prerecorded Disks. Polystyrene or polyvinyl chloride with stabilizers. 7 inches. 45 rpm
=Further Reading=
* Northeast Document Conservation Center. 2014. "A Hefty Challenge for IRENE: Working with Delaminating Lacquer Discs". IRENE Seeing Sound Blog, August 12.