B&W negs on Fuji CA paper

My local mini lab is exclusively colour as most are nowadays but they will print B&W negs onto Fuji CA paper and to be fair do a very good job. Just as an experiment I got them to make a print from a B&W neg and compared it to my own print on Ilford MG IV.

In daylight and only if you have both prints side by side the Fuji print looks slightly greenish and makes the Ilford one look quite brownish/warmish by comparison although in reality it's fairly neutral. My developer( Nova) gives the prints a look which is only just on the warm side of neutral. Without a side by side comparison the Fuji print might not seem to be greenish. It also lacks some contrast as well. I assume this to be due to not being able to alter the Fuji CA's contrast.

Anyway now to the interesting part. This difference in appearance which is very noticeable in daylight in a side by side comparison seems to disappear after dark when the two prints are examined under fluorescent lighting. I looked again under tungsten light and the difference, observable under daylight, re-appears albeit to a lesser extent.

Anyone care to give an explanation of this phenomenon?

Thanks

pentaxuser

Three effects are seen here and it is hard to distinguish between them.

One is the presence and absence of fluorescent dyes. Sunlight has lots of UV and some tungsten lights emit UV light. In any event, this makes a print shift on the yellow - blue axis.

Second is the fact that some dyes shift to longer wavelengths or shorter wavelengths (bathochromic or hypsochromic shift are the technical terms). This may not take place in all dyes to the same extent and so the balance may appear to shift.

Third is the unit neutral of any image. Even silver is not 'neutral' but has a definite color cast to it that varies with how it is produced. A dye set had humps and bumps which your eye is 'tricked' into interpreting as being neutral in a perfect blend, but which is not pefect. So, you see one or another dye predominate as illuminant shifts.

This last item is involved with fluorescent lights which have a discontinuous spectrum consisting of peaks and bumps which may emphasize any imperfections in the dye set.

To describe it more fully, one would need to scan a neutral step wedge with a spectrophotometer using different illuminants and then the effects could be separated out and described more fully.

Sorry, but that was a very technical question you answered.

PE

That helps a lot. Thanks PE. My conclusion is that if you need a set of small holiday snap prints from B&W negs in an hour which are unlikely to be on show and framed or a keepsake then a good colour mini-lab, using colour paper might fill the bill.

Special occasions and prints that are longterm mementos however demand the right stuff. My cousin had a set of B&W fibre prints done for his wedding in 1969, using of course trad B&W film and medium format to boot. They still look superb. Better than the groom does after 39 years!

It has raised one more question now that your answer has extended my thinking. To what extent can you avoid the issues raised in my thread of having B&W printed on to colour paper by using C41 B&W film and in terms of the best for this purpose does Kodak rank number one? It is often claimed that it was designed for colour paper whereas Ilford XP2+ was not and where in any ranking does Fuji B&W C41 film come, I wonder?

Thanks

pentaxuser

I cannot answer those questions for you.

I know that our design criteria for Ektacolor paper was to minimize or eliminate those effects I described as far as possible, and so dyes that behaved in the manner that I described above were eliminated.

I do feel that the current Endura paper makes a good neutral, but it shifts hue subtly on the warm to neutral axis depending on illuminant. That is probably due to the new dyes they use to improve image stability. But then that is my subjective impression. I have not run exacting tests to confirm or refute it.

PE