Records

=Records or Disks=
==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==
1887: Berliner Disk 
A Matrix recording. Glass covered with lampblack; traced and lacquered; photoengraved. Easily breakable. 
1888: Wax Recording Blank 
A Matrix recording. Zinc disk coated with wax; traced; etched with acid
1888-1897: Berliner Record 
A prerecorded disk made from a matrix. Hardened latex (latex rubber vulcanized with sulfur) also known as vulcanite; easily malformed.
Circa 1888-1897: Celluloid Disk 
A prerecorded disc made from a matrix. Cellulose nitrate; brittle.
1896: Solid Wax Disk 
A Matrix recording on solid wax. 
1897-c.1948: 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.
1906: laminated shellac disk 
Like the shellac disk but with a core of heavy cardboard.
1930s: Aluminum Disk
Either a Matrix or instantaneous recording. Aluminum. 12 inches or smaller.
1934: "Acetates" or Lacquers or "Direct Cut Disks" 
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. 
early 1940s: Dictation disks
Instantaneous recording. These are so-called "plastic" disks under the names Voicewriter, Gray Manufacturing, Audograph.
1948: Long Playing (LP) Disk 
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. 
1948 or 1950: 7" Microgroove Disk or "45s" 
These are prerecorded disks. Polystyrene or polyvinyl chloride with stabilizers. 7 inches. 45 rpm
==Conservation Practices==
==Conservation Products & Supplies==
==Equipment==