"tm" wrote:

I did not paint any of the wood and I've not
experienced any adverse affect while printing
with my enlarger. Thus, I do not see any reason
to paint a darkroom black ...

There are several sources of 'stray light' (light you don't
want) when enlarging:

1) Light leaking from the enlarger

a) negative carrier
b) lamp housing
c) lens board or lens turret

2) Light leaking (not quite the right word) from the lens

a) internal lens reflections (not a big deal w/ coating)
b) Imaging of inside of the lit (by the negative) portions
of the lens bellows/cone and negative carrier. If possible
twist your head and take a look up the lens - scary.

3) Light reflected from the paper, illuminating the room,
especially the ceiling and hence the paper. If you have
a white ceiling take a look up when enlarging.

The result is that the whole area around the enlarger is well
illuminated with white light - if your darkroom was this light
you _know_ your paper would fog.

The effect is variable:

The effect from (1) is proportional to the exposure time and
negative density - the amount of fogging light is constant and
the longer the exposure time the more fog.

The effects of (2) may change with head height as more of the
light falls on the enlarger column or room walls.

But generally the fog from (2) and (3) are constant for all
negatives and magnifications: they are proportional to the
amount of light-seconds to expose the paper which, if
paper sensitivity is fixed, is generally constant.

In sum, just about all the fogging light hitting the paper
first bounces off the ceiling and walls. Painting them
black will reduce the amount of fog. (3) light from the
enlarging paper, and often the greatest contributor, can
only be mitigated by painting walls and ceilings black.
Reducing (2b) requires a bit of flocking/painting inside the
enlarger.

Now, how much does this matter?

If you are making murals you will find it is almost
impossible to get clear highlight. The light leaking
from the enlarger, that has no effect in a 20 second
exposure, fogs mightily in a 10 minute exposure. Also
the entire darkroom becomes the enlarger's cubicle and
would need to be painted black to keep fog down.

Can you see it? Do you care? Only one way to find out:

1) put a clear negative in the carrier, place
two overlapping coins/opaque things in the
center of the paper.

2) make a middle grey exposure

3) place a coin on the center of the clear film in
the carrier. The coin should not cover more
than 1/3 the negative area.

4) Remove one of the coins in (1)

5) Make another exposure equal to (2)

6) Develop

7) Any difference between the overlapping coins is the
highlight effect. Any difference in the shadow of
the removed coin is the mid-tone effect.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/