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#112
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On 7 Mar 2005 02:10:07 -0800,
wrote: Jean-David Beyer wrote: LR Kalajainen wrote: It takes at least 24 hours of soaking before the brighteners begin to wash out. In prints left in water overnight from, say, 11 pm until 8 am, the brighteners aren't affected--- at least I've not been able to tell any difference visually. Brighteners begin to wash out right away, ... Just as well. The sooner they wash out the better. I recall reading that the brightener titanium dioxide contributes to peroxide production with attendent image degradation. think whiteners are more used with RC papers. To easy to measure loss of whiteners for there to be any question. Dan mar905 from Lloyd Erlick, How long do the brighteners last? Given an ideally processed print, whatever that might be, do the brighteners have a lifespan? Will they last as long as the print, or 'wear out' some time before the print dies? Will the print become less acceptable at some time during its life because the brighteners have stopped working? If the print is otherwise in good condition, but the brighteners are worn out, is the print less acceptable? Must darkroom workers make prints expected to be 'good' only as long as the brighteners are present, presuming the brighteners stop working at some time. Since the brighteners work only under some amount of ultraviolet light, what about those of us who display prints mostly under incandescent light? Is there an ideal level of UV, and an ideal type of UV, for print display? Do the paper manufacturers specify that level? Just curious. regards, --le ________________________________ Lloyd Erlick Portraits, Toronto. voice: 416-686-0326 email: net: www.heylloyd.com ________________________________ -- |
#113
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To your eleventh question; yes to the first part but for "type of
UV" I've no preference. I suppose it would depend on one's mood and what for that after dinner drink. Why be so concerned, you use a warm silver Ilford MG. Warm silver against a steely blue paper or at the very least a most brilliant fluoresent WHITE! I'll check into it. I may be right, an RC additive. BTW, I'm working with that Ansco/Beers A. Last night I mixed up another 1/10th batch and my first Beers B; a little of the A plus all the B and I've Beers # 7. Dan |
#114
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#115
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wrote:
I've checked into it. A lengthy article by Ctein in Photo Techniques does include paper coatings. snip And that's it; barium sulfate - FB, titanium dioxide - RC. Dan Just to be clear, those aren't the "brighteners" that we've been talking about in this thread. They are the coatings that make the paper whiter, yes, but they don't convert UV to visible light. FB papers use barium sulfate, whether they include brighteners or not. I've never heard of the barium sulfate or titanium dioxide washing out of paper. I expect that the paper would have to disintegrate for that to happen. Titanium dioxide, though, has caused problems with RC papers. Supposedly this has been fixed. -Peter De Smidt www.desmidt.net |
#116
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wrote:
wrote: I'll check into it. I may be right, an RC additive. I've checked into it. A lengthy article by Ctein in Photo Techniques does include paper coatings. Apparently I'm correct. The "photoactive" compound titanium dioxide, "whitener", is used with RC papers. Barium sulfate, baryta, is used with FB. The sulfate does not work with polyethylene. All as of 1997. Those compounds are not "photoactive" as brighteners. They are merely highly reflective sizing used in the paper to make it a bit more opaque and to increase the reflectance. They play little or no part in the effect under discussion he the brightening of the paper by shifting invisible (i.e., long wave ultraviolat) light into the visible spectrum. Does one or the two of those wash out? TiO2 is insoluble in water, so it does not wash out. BaSO4 is nearly insoluble and does not wash out to any appreciable extent. Or as some other suggested, is something else going on? Or, as I now suggest, nothing is going on that need concern us. Dr. Henry's tests with ultraviolet light may have been no more than curiosity getting the better of him. Did he compare baryta with the dioxide? Rather than second guessing Dr. Henry's tests, why not just read them? He writes very clearly. He did not compare Barium Sulphate vs Titanium Dioxide. There was no need to. He was testing brighteners, now paper sizing agents. That would be testing RC vs FB. And that's it; barium sulfate - FB, titanium dioxide - RC. Dan Which sizing is used in the paper (BaSO4 vs. TiO2) has nothing to do with this discussion of brighteners. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 21:30:00 up 50 days, 5:47, 3 users, load average: 4.33, 4.31, 4.20 |
#117
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Jean-David Beyer wrote:
Which sizing is used in the paper (BaSO4 vs. TiO2) has nothing to do with this discussion of brighteners. I don't recall Ctein using the word brighterers. The two whiteners he does mention. He does not say that the dioxide does fluoresce only that it will on exposure to light contibute to peroxide production. Do you know for a fact that the dioxide does not fluoresce? I suppose Dr. Henry mentions both as they are, in your mind two distinct entities. He does mention whiteners.? Dan |
#118
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wrote:
Jean-David Beyer wrote: Which sizing is used in the paper (BaSO4 vs. TiO2) has nothing to do with this discussion of brighteners. I don't recall Ctein using the word brighterers. The two whiteners he does mention. He does not say that the dioxide does fluoresce only that it will on exposure to light contibute to peroxide production. Do you know for a fact that the dioxide does not fluoresce? I suppose Dr. Henry mentions both as they are, in your mind two distinct entities. He does mention whiteners.? Dan IIRC, he does not mention whiteners. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 06:30:00 up 50 days, 14:47, 3 users, load average: 4.26, 4.21, 4.12 |
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