In 13 Ghosts (1960), the gimmick wasn't "pure" 3-D, but was as follows:
In the film, the (deceased) character of Dr. Zorba had invented special glasses that allowed the wearer to view the apparitions. Whenever a character in the film put on the glasses, that was the signal for the audience to put on theirs. If you didn't wear your glasses, the onscreen ghosts were not visible.
All prints shown on TV or released to home video have been reprocessed to eliminate the need for the special glasses.
Pity.
Signor V.
"For me, there's only my wife..."
"Sure I cook with wine - sometimes I even add it to the food!"
"When life itself seems lunatic, who knows where madness lies?"
"It was a grass harp... And we listened."
"Do any human beings ever realize life while they live it? Every, every minute?"
"No. Saints and poets, maybe... they do some."
| 
