For starters, the only 78s that are truly unbreakable are the ones made for mood music libraries (Chappell, Boosey & Hawkes et al) in the 50s and Capitol's "Superflex" kids records in the 40s. Everything else can be cracked by putting your thumbnails together and pushing up..experimenting this way on unwanted discs is a good way to learn which ones will and which ones won't. Even Decca LPs from the mid 50s to the early 60s will fail this test.
Other than that, it may be a matter of what country you're in. Canadian plants kept 78s into 1960 and all but Quality used shellac, while Quality's vinyl was easily cracked.
dl
MATSUBAYASHI 'Shaolin' Kohji wrote:Hi, and happy new year all,
I'm just curious - what can I distinguish shellac 78rpms from other thick vinyl-made 78rpms, not only by reading labels saying such as "Merco Plastic" or "Non-breakable"?
The last era of vinyl 78rpms can be easily distinguished just because they are very thin and flexible. But other type of vinyl 78rpms, as well as very early LPs, are not flexible and rather thick. I've been wondering whether the last era of thick 78rpms (late 1950s to early 1960s, for example) are actually made either of shellac or thick vinyl.