Richard wrote "If it works the effect is to lower the contrast of the highlights. Actually, the stain _is_ linear in that it is exactly proportional to the silver density, however, its effect on the paper depends on the stain density so its effect is greater for highlight than for shadow areas." .....its effect on the paper depends on the stain density so its effect is greater for highlight than for shadow areas..... Yes its effect is linear on the film, but is its effect on the paper linear? Jonathan Ayers [mail1@xxxxxxxxxxxxxxxxx] -----Original Message----- From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow Sent: Tuesday, May 08, 2007 9:19 AM To: pure-silver@xxxxxxxxxxxxx Subject: [pure-silver] Re: DELTA 100 AS REPLACEMENT FOR Tmax 100 ----- Original Message ----- From: "Janet Cull" <jcull@xxxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Tuesday, May 08, 2007 5:38 AM Subject: [pure-silver] Re: DELTA 100 AS REPLACEMENT FOR Tmax 100 Wow! Beautiful. Is it that film developer that is a stain dev. or the paper? I've never heard of such a thing. On May 7, 2007, at 11:55 PM, mail1 wrote: > Bob, Very nice. I have explored Barry’s developers. The > non linear > blue blocking stain has posed interesting changes in the > variable > contrast filters interaction with paper contrast. It has > taken me > some time to understand this relationship. In fact this > has created > an interesting diversion from my day to day activities. > Grade 2 > filtration is no long grade 2. > > Jonathan Ayers [mail1@xxxxxxxxxxxxxxxxx] > It is the film developer which causes a stain image. By "blue blocking" above is meant that the stain blocks blue light. Because variable contrast papers have a component which is sensitive to blue light and another which is sensitive to both blue and green the effect of the stain is to vary the contrast depending on the density of the stain. At least, this is the theory. If it works the effect is to lower the contrast of the highlights. Actually, the stain _is_ linear in that it is exactly proportional to the silver density, however, its effect on the paper depends on the stain density so its effect is greater for highlight than for shadow areas. Most staining developers contain Pyrogallol as the developing agent but other developing agents can also generate a stain image, it depends on the developer formula. Because the stain is produced as the result of the reaction products of the developer the amount of sulfite in the formula is important. Sulfite tends to reduce the amount of reaction products so staining developers can not have too much sulfite or the stain will not appear. This tends to make staining developers relatively short lived. Note that other anti-oxidants than sulfite are used in developers but they all have the same effect on staining. Staining developers were quite popular until the 1930's when non-staining developers began to be preferred because their results were more predictable and consistent. Except for the highlight contrast reduction effect there are probably not many virtues to these developers now. One problem is determining the effective density because it will depend on the spectral sensitivity of the printing material. Some users beleive that the stain image reduces the visibility of the film grain. The stain image from Pyro type developers is a _pigment_ not a dye and is probably more stable than the silver image. Another effect sometimes seen when Pyro developers are used is a slight increase in edge sharpness (acutance) beacuse the Pyro also differentially hardens the gelatin causing an image-wise variation in index of refraction. --- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx ============================================================================ ================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there. No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.467 / Virus Database: 269.6.6/794 - Release Date: 5/8/2007 2:23 PM No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.467 / Virus Database: 269.6.6/794 - Release Date: 5/8/2007 2:23 PM ============================================================================================================To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.