Low contrast with bounced light source?

I had a strange experience in the darkroom this evening. I was contact printing a 5x7 negative, which perhaps has lowish contrast but not to an extreme degree. I had a couple of tries at printing it on Ilford MGIV, with a 7.5W bulb pointed at the ceiling, which I've found I have to do if I want exposure times longer than a few seconds.

The results, not to put too fine a point on it, sucked; murky grey things with no blacks or whites in the image area. Increasing the exposure to get the blacks black resulted in a ridiculously dark, no-contrast print; decreasing it to get the whites resulted in a ridiculously light, no-contrast print.

I made some disgusted noises, then flipped the light to point down, swapped in a 15W bulb, and made a straight print on Fomalux (a contact-speed chloride paper). The result was quite nice; I had to do a second print to burn in the sky, but even the initial straight print was quite acceptable apart from that---in particular, it looks like a print with normal contrast.

What's going on here? Both papers supposedly print at grade 2 with unfiltered light, so why would I be seeing a difference in contrast? Is a bounce from an off-white ceiling likely to be changing my colour temperature so much that the Ilford paper is printing at a lower grade than expected? (I've done it this way before and gotten decent prints, though come to think of it, I *did* have to filter to a higher grade than I expected sometimes.)

Is the bounced light my problem, or is there something else I'm not thinking of?

Thanks

-NT

Contrast difference between a point light source (bulb pointed straight down) and a diffuse light source (bounced light)? -- probably not to the degree you saw.

Yellowish light source bounced of a yellowish white ceiling acting like a lower contrast filter? -- more likely. I shot a wedding, bouncing the flash off a off-white ceiling. Thankfully the printer worked with the prints to get rid of the yellow cast!

Vaughn

Your 7.5 w lamp is Very red/yellow to begin with. Even a 100 w bulb puts out something like 2800 k (don't have precise data available now). As the wattage diminishes, so too the temp, and you are getting into serious red territory. Probably part of the reason you get longer times, because a proportion of the light output just doesn't count. What light does count is probably pretty much equivalent to a 00.

Try laying a sheet of white plexiglass over the printing frame,
and aim the light right at it.

(I use milkglass, but I've been accumulating the stuff for 40 years).

When I replaced the yellowed cardboard inside of the 4x5 diffusor box of my Ilford 500H multigrade head with new, whiter, cardboard, I had a small but noticeable shift in contrast and light output. So yes, the bouncing on a non-neutral ceiling, could well make the difference besides the other good remarks here.

Thanks for the help, everyone. It sounds like the bounce really is at fault. I'll try to cook up some sort of arrangement for reducing the light---I hesitate to put something over the printing frame, because then I can't see the image to dodge/burn, but I think I can rig something to hold a sheet of plexi up at the light itself.

-NT