De-Warping 78rpm Records

  • A discussion on de-warping 78 rpm records gave some excellent information recently on the 78-L list. One member of the list provided the following, informative step-by-step guide:

    I have a thick marble plate, about 1 inch (2.5cm). It's a marble plate for serving cheese, actually. I put it in my oven at about 80 degrees Celsius (has to be controlled by thermometer!), and I leave it there for half an hour to gather up heat. (Don't trust the temperature setting for your oven!) Then I take the record out, put it on the marble and wait a couple of minutes. Next I turn the record around and wait again until I can feel that it has softened a bit. This is the moment when you have to watch the record closely. Because it should not get too soft, and it should also get perfectly flat. So I take the record off the marble plate and put it on the work surface in the kitchen, which is cold, of course. There, the disc can harden slowly. You may put something on the disc to assure that it stays flat until hardened, because some dished records have the tendency to 'warp' back into the original state while cooling down! Works perfectly, also for aligning the hair line cracks of 78s so as to eliminate the ticks!

    Another suggestion related how glass plates were better at conducting heat to help flatten 78 rpm shellac records:

    I have two pieces of plate glass both 12 inches square and a quarter inch thick. I put the 78 records between the two pieces of glass and place it near or over a stove about six inches from the heat source. During summer, some people put them on the dash of a parked car with the windows up. Do not add weight, just use the glass only. It can take two to four days depending on how warm your house is. But I must stress - Do not add weight! Using an oven is often suggested for de-warping 78s. essentially, heat is the only thing that can soften the shellac in order to reshape it - but often, there is contention over what is a suitable heat source and at what temperature should a record be set at.

    Another reader offered the following description using an oven:

    I put the oven at 200 degrees and place a record on a flat cookie sheet. Depending on record type, 3 to 4 minutes later the record is soft enough to relax to be flat on the cookie sheet. Then slide the record off onto the counter to cool. I always put something on top of it so the edges don't bow back up. The temperature differences of the counter and air side will make the record want to bow a little during cooling and this stops it. This method comes with a major warning. Every oven is different. I have never actually put a thermometer in the oven to see what the temp actually is. The 200 setting is higher and the time longer than I've read elsewhere but that's what works for me. So you'll need to do some test cases on some less expensive records. The record will go from not soft yet to stuck on the cookie sheet in short order if you aren't paying attention. This method is also a lot faster if you have many records to de-warp.

    Of course, the dooms-dayers have their day - and some members of the list are prone to express their fears with de-warping 78s thus: THERE IS GREAT POTENTIAL FOR DISASTER WHEN YOU PLACE RECORDS IN AN OVEN OR OUT IN THE SUN... But one suggestion was very informative:

    1. Make a wooden frame 14 inches square, using wood 8-inches thick
    2. Get a simple light socket with a mounting flange to hold a 25 watt light bulb in a vertical position. Place the frame over this
    3. Get two squares of plate glass. making sure they are completely clean
    4. Put the first piece over the frame and place the warped record on it. (This glass should be a least 2 or 3 inches above the light bulb)
    5. Put the second piece of glass on top of the record
    6. On top of this use just a little weight (A stack of 10 78s worked well for me)
    7. When adding the weight, introduce it gently to avoid the possibility of snapping the warped record
    8. Now turn on your 25 watt light bulb and the process begins
    9. Allow several hours for the gentle heat to do its work (I usually set it up and let it go all night)

    IMPORTANT: When you turn off the light, DO NOT try to see what's happened until the record has had an hour or so to cool and regain hardness. This procedure always gave wonderful results with the record coming out straight as a die.


1 comment
  • Tom Jardine
    Tom Jardine I experienced a disastrous event years ago when de-warping using the two pieces of glass and a low temperature oven. My scarce and newly acquired limited edition HMV AGSA John McCormack set had one particularly warped record. What I didn't realize was...  more
    October 21, 2014