Unknown black and white film

[wallacjm]

While cleaning out a darkroom at a school, I found a bulk film holder with film in it. I did not find the box that the film came in. It was stored in a cabinet under an enlarger. I am going to load 12 exp and test it to see if it any good, but is there a procedure to find the speed of the film when you don't have the information?

Thank you

 

[AnselMortensen]

Try just developing a short roll of it without exposing it.
Pretend it's Tri-X, use that development time/temperature.
When it comes out of the fixer, rinse it off & read the edge lettering.

 

[reddesert]

Films can lose sensitivity over time, as well - more so for higher speed films. If you're going to develop it, you might as well take a series of test exposures. Pick some typical scene with a range of brightnesses and take exposures as if ISO 12 to ISO 800, say, stepping by a factor of 2 (one stop) between exposures. Develop at some nominal time (as if Tri-X, as AnselMortensen suggests). Hopefully you'll see a fairly obvious trend from over to under exposure.

 

[Kino]

12 exposures.

A person with a grey card in full sunlight at around 10am or 2 pm to avoid high noon.

Set your lens at f16 and start at 1 second. Take 1 exposure for each division of your shutter speed selector.

1, 2, 4, 8, 16, 30. 60, 125, 250, 500, 1000 and 2000th of a second. If your speeds top out at 500th or whatever, then start closing down the f stops one at a time until you run out of film or f stops. You are probably already out of range by then anyway...

Process the film as AnselMortensen suggests, something like mid-scale for Tri-X @ 68F/20C in D-76 1:1 or your favorite developer; probably 8 minutes.

Your best exposure will indicate an approximate ASA/ISO for that film AT THAT TIME/TEMPERATURE/DEVELOPER combination. You may have to estimate between shutter speeds, but a general ballpark sensitivity will be established.

I am guessing you will probably fall in the 16 to 500 range, but you never know.

Also, look at the edge markings!

 

[AnselMortensen]

Five bucks says it's Tri-X.

 

[koraks]

Also, look at the edge markings!

Maybe start there. Snip off a piece of the film (in the dark, unexposed film), process it and check if there are any edge markings that give away its identity. If so, take it from there.

Nothing wrong with doing some test exposures, although personally I'd just shoot a frame at EI25 and one at EI100 and call it good. Inspect results and take it from there.

 

[albada]

I agree with @koraks. Try shooting five frames at EI 400, 200, 100, 50, and 25. The first frame with adequate shadow detail is the correct EI.
Try developing as if it were Tri-X, and fixing as if it were a T-max (longer fix time).

Mark

 

[Don_ih]

2 inches of film in working strength paper developer for 4 minutes should show you the numbers. You want strong development, since those numbers can sometimes be faint with normal developing.

But I'd shoot a short strip similar to how @Kino suggests. Kill two birds with one stone. In that case, develop in paper developer for 3 minutes to get an accurate idea of speed.