Photo-Lettering wasn’t the only type provider to issue effect typefaces with pattern fills (see Papirtis Intrigue, Davison Kaleidoscope, etc.) in the second half of the 1960s: Burst Caps is a related design that was carried by Franklin Photolettering, Lettergraphics, and Solotype. Its origin is unclear, but it was used already in 1967.

Burst Caps here can be seen on the cover of a science fiction novel by Rena Vale (1898–1983), published by Paperback Library in 1970. No typographer is credited. The cover art with the Rorschach test-like mushroom cloud is by Richard M. Powers.

From the back cover:

When the Yellow Alert flashed, all flights from O’Hare Jetport were postponed indefinitely. Of the thousands of people waiting there nervously, only fifteen escaped in the sudden nuclear blast that destroyed life on Earth. The fifteen lived because they had been transported 50,000 years back through time – to just before an earlier Doomsday.
Who brought them there? Why did the chosen few include a hired killer disguised as a priest, a religious fanatic, a woman who poisoned her husband’s blueberry muffins, a slumlord, a lecturer and a farmworker? And what did their kidnappers mean by telling them they were in training for The Day After Doomsday?

[More info on ISFDB]