On Sun, 08 Feb 2004 23:28:49 +0100 Thomas Holm wrote: > When you "mix and match" ink and substrates from different vendors it will > most certainly be almost impossible to obtain permanence data for the >chose combination. For example on an IRIS on one specific inkset and a >certain paper you could get upwards of 80 years, change the ink or paper and you > could be looking at months instead...
Right on! To make it worse, a test may be commissioned to 50% humidity, 60% humidity or whatever. Neither of which relate to the reality of a print's normal display conditions (which would have varying humidity). And humidity is only one of many test factors. The most honest manufacturer spec I have seen is by Jon Cone (Piezography carbon 'inks' http://www.inkjetmall.com/store/info/1000-hours.html#explain), which specify a test of varying humidity between 20% - 90%. He says - 'RIT and Wilhelm allow a density fade rate of 30% to arrive at their ratings endpoints. However, the threshold at which humans can detect fade is 5%. The deltaE figures represent a measurable difference in color. The threshold for humans is 2.............We believe that side-by-side comparisons of actual fade (density decrease) and color shifting (deltaE differences) is the best way to determine how well an ink performs.' > (my rule of thump is usually to divide longevity by 5 <G>). This is interesting Thomas, is it based on experience, or are there any references I could follow up? On Sun 8 Feb 2004 23:10:29 +0000 Richard Kenward wrote: >When one talks of permanence and fading, one has to ask what criteria is >used to determine when a print has faded enough to say yes this print has >faded? There is nothing on the Wilhelm site that I can see that deals with this rather >important issue. Richard - Try http://www.wilhelm-research.com/pdf/WIR_Ep9600_2003_11_01.pdf, (p.4), but bear in mind that every commissioned test could be using different criteria. Your question is interesting - by 'fading' do you mean 'colour difference'? A print can 'fade' quite a lot before the human visual system can detect it. A colour difference of less than 2 delta E is considered imperceptible, 2-5 acceptable in one respected study (Stokes, Fairchild and Berns 1992). There are different percepual responses to pictorial images and pigment patches, and other methods of measurement (e.g. delta E94, based on D65 brather than D50). Perception of any colour is massively influenced by surrounding colour, both in subjects and images. There are other aspects not generally considered in the fading debate, such as paper yellowing, mentioned among others by Epson (http://www.dpandi.com/resources/permanence/cpd-15334_1102.pdf). I sell fine art prints through an art gallery, so am pretty concerned about what I say to customers about longevity. Most don't have time to listen to the 5 minute lecture, never mind the 2 hour one! I've had to conclude that I can't honestly say anything absolute, and on my website have a page briefly discussing the situation non-technically. A scientific test result for a given pigment/paper combination doesn't mean that one can then apply this to one's own product because the display conditions are bound to be different. The best I can say is that there are no trade standards for any supplier to rely on, but that my pigment prints should last for decades, certainly many, many times longer than basic inks, before fading becomes unacceptable to most people. In the end we may be left with the ridiculous situation that a longer lasting combination with more honest and stringent conditions could actually achieve a 'lower' rating than a shorter lasting combination with less stringent test conditions. My brother runs a major UK ink manufacturers, and I know he sticks prints on the window to see if they fade as well as having Wilhelm tests done! Tony Riley (Kendal version!) www.photosightdesign.co.uk www.sharpedgegallery.co.uk =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
