Producing any color on a dichro head

[bvy]

I have an Omega C760 enlarger with dichro head, and I've been experimenting with duochrome enlargements from black and white negatives. 90M+110Y gets me pretty close to gray with most black and white films when enlarging to Fuji CA paper. So I could use this filtration to produce a regular black and white enlargement (granted it will be low in contrast and have some slight tint, but for this exercise it's close enough). Now suppose I wanted pure red midtones and shadows. I would filter out magenta and yellow in tandem. But how much? 40M+60Y? 0M+20Y? Start dialing up the cyan?

I've done some experiments already, but the exposures were all over the place since changing filtration changes exposure. Before proceeding again, I'm thinking there must be a way to "map" a given color to a filtration if the gray filtration is known (for the paper, film and process in use). Thoughts?

 

[darkroommike]

Do a color "ring-around", this article explains the how to, https://www.ephotozine.com/article/making-a-colour-darkroom-ringaround-chart-4792 .

 

[sfaber17]

If you want red, you should dial down equal M and Y, but your dials may not reflect density linearly, so it would be best if you used a color analyzer to dial down equal density.

 

[bvy]

Thanks. I don't have a color analyzer unfortunately. Also, I've done the ringaround for correcting/adjusting color casts when printing negatives, but for this exercise, the changes were too subtle. It seems like there must be some "extreme" past which I'm only introducing neutral density. Is it 50cc's? 100cc's? If it's 100 and my gray filtration is, say, for simplicity, 100M+100Y, then I would expect 0M+0Y to produce red, 100M+200Y to produce green, etc.

 

[darkroommike]

In the past my neutral filtration was something like 50M+50Y Adding or subtracting just 30 units is a push, 50 units is a big push and 100 units is a shove. I can not think of a case where you'f have all three colors in a filter pack. Subtractive printing is not linear, since the dyes are not perfect. Look to your color head, rarely will you see a color head with more than a value of 200, the Durst heads have smaller numbers but the scale is different. Take a piece of paper and divide it into six segments. Expose it to the maximum value of each of your filter channels. 200Y, 200M, 200C, then 200Y+200M (200R), 200M+200C (200B), and 200Y+200C (200G). I printed a black and white silouette in front of a fireplace once with 100 Cyan (Durst M601 max setting) looked just like a color fireplace shot.