When magnetic tape was first spliced, some editors actually used scissors so that the shear angle could be varied to create the desired crossfade length.
However, for speed and standardization, editors preferred to use an Editall block, which was similar to a carpenter's miter box. Blocks for ¼" tape have a 45 degree angle for the cut. This would give a 33 millisecond crossfade at 7 ½ ips, a 16 millisecond crossfade at 15 ips, and an 8 milliseconds at 30 ips. The block would hold the tape and guide the razor blade so that the splice could easily be made.
The Editall blocks for 2" tape have a 87 degree angle cut, which was the proper angle when they used cut 2" quad-scan videotape. It's a much steeper angle than the ¼" block, but works well for 2"audio tapes, since a shallower angle would create too big of a timing difference between track 1 at the top of the tape and track 24 at the bottom.
Magnetic film with sprockets was generally edited with a guillotine splicer that cut straight across the frame line with no angle. Therefore, film editors would usually scrape the edits with a razor blade to flake some of the oxide off, so that the sound would fade in. This created a virtual angle for the edit so that the start of the track had a very quick fade-up, and thus prevented pops.
