
I blackened the blank using a Sharpie marker, then did the first impression and got all the spaces.

I filed each of the five pin marks lightly. After this, the first mark to appear in on Pin 1... note that there is some striations from improper filing on the other pin locations. I did learn one thing: The key is to decrease pressure at the end of the forward stroke to get a smooth cut surface.
(The other round markings at front slope of Pin 2 and 3 in the image are not impression marks.)

But marks don't always appear. I've had to re-impression the key a few times. Sometimes I get confused because I see "burnishing marks" and not dots/dimple marks. I rub those away with light file strokes. I'm not always sure what I'm looking for... and sometimes I get less and less sure when clear dimple/dots don't appear, even after multiple attempts.
Pete
Sioux Falls SD