KLUDGE@AGCB1.LARC.NASA.GOV (01/02/91)
On 78's: Most of the 78's which were called "shellac" were actually unplasticized vinyl. If you compare a WWII era disc with an early hill-and-dale Pathe, you will find they were made of very different materials (the Pathe is made of actual shellac, which is slightly softer when warm). Vinyl was developed quite early, but without the plasticization process developed in 1927, it is quite brittle and has poor cohesion. On 78 preservation: First thing to do is get them out of the attic. Atmospheric water and oxygen are your two big concerns. Water in the air will cause cracking. Heat and light will cause the material to dechorinate, and in conjunction with atmospheric water will form minute HCl residues. Get the record out of there. Wash them well with something alkaline (dish detergent is okay. I use something called "DeContam" which is designed for microelectronics resist and wafer cleaning, which leaves less residue, but the dish detergents do a good job and are easier to get). Put them in new, clean liners (The Discwasher ones are excellent, though the Tyvek ones which are sold for library use are less expensive. I worry about the fibre pattern on Tyvek, but I don't have anything to back my worries up with, so don't let me stop you). And keep them at room temperature in a low humidity area. If it's comfortable for human beings, it should be okay. 75', 50% RH is what the book says, and it's worth trying for. Don't worry about the cleaning water causing cracking; it may, but it'll do far more good than harm. But do towel the records down if you can. --scott