Image dyes and stability
There have been a lot of comments on image stability here and elsewhere regarding color materials. I have made one post here with a rather lengthy summary of the subject, but here goes again with more information.
There are two classes of dyes used in color photographic materials. One type is the Azo dye, and the other type is the Azomethine dye. The Azo dyes are made and then either coated, or imbibed into a coating as in Ciba/Ilfochrome and Dye Transfer respectively.
In the Ciba/Ilfochrome material, the dye is incorporated by immobilization in one sheet of material, a negative image is formed, and the dye is bleached along with silver leaving a positive dye image. In dye transfer, a positive silver and gelatin image is formed by using a hardening developer. This hardened gelatin is in relief. Dye is imbibed into the film from solution and is transferred imagewise to a mordanted paper. Both of these processes can use almost the same dyestuffs and can achieve the same level of dye stability.
A further improvement in dye stability can be achieved from Azo dyes by complexing them with a metal. This is somewhat different than just mordanting the dye in place. It is an actual electronic bond with they dye which causes a huge improvement in dye stability. These so called "metallized dyes" were under development at EK when the entire diffusion transfer and dye transfer projects were cancelled.
These products, in general, have the highest stability to light, heat, air, pollutants and humidity.
The next class of dyes are the Azomethine dyes, or so called chromogenic dyes used in all films and most color papers today. A coupler is incorporated into the coating and the dye is formed by the color developer.
These dyes are more subject to fade than Azo dyes, from heat, light, air, pollutants and humidity. Much research has been done on preserving these in film and paper. The results have been gradual improvement over the years of the stability of films and papers.
Methods to improve Azomethine dyes include forming micro crystals of dye in the coating (Kodachrome uses this and it blocks fading well). Antioxidants such as vitamin E derivatives can be used very effectively added to the emulsion or even as a sub-group on the dye itself. In addition, use of UV absorbers have been used for years to block unwanted radiation from films.
Recently, it has been discovered that certain chemical distortion can be achieved in the dye and this prevents, or blocks dyes from being attacked by outside influences.
Kodak and Fuji have both published reams of articles and patents on this type of work, and have pretty much reached a parity in dye stability which is just a tad below the achievable level of the Azo dyes. It may even be on a par with the Azo dyes.
But now comes the problem.
How do you define the test for image stability in terms of light intenstiy, spectrum, and also heat, humidity and pollutants. Beyond that, how do you determine whether a print is unusable or undesirable due to some sort of deterioration.
These definitions have led to huge differences of opinion in the industry as to who is right about their products. The bottom line is that no one answer exists, and no one company has a monopoly on being right or wrong.
It may be counter intuitive, but the average home gets more light in higher latitudes than on the equator but it is true, due to the position of the sun and the surrounding levels of foliage during the different seasons. In fact, in winter in the norther hemisphere, when all the leaves are fallen, an average home gets more light than in the summer. So the true cycle is hot, humid and dim to cool, dry and bright when in the north and at the equator it is hot, humid and medium bright all the time. This cycle, when not tested, is a problem when reporting data.
Among other things, accelerated tests do not project easily back to slow normal aging due to reciprocity. Reciprocity rears its ugly head even in dye fade by any means.
Fade in homes in the Andes have been found to be influenced by higher UV, lower Oxygen, and lower pollutants except in big cities where fade increases due to pollutants.
Kodak has run tests world wide to accumulate data on these conditions and I know as one of the individuals reporting on this data internally that they have tried to make it as honest and straightforward as possible. I'm sure Fuji has done the same. The differences though are in the details.
Now as for evaluation, how do we say a print is unusable. Is it unusable after 5% dye fade or 10%, or is it unusable if only one dye fades even if that fade is 1%. Well, it turns out that even this is a difficult call. A 10% fade that is even in all dyes sometimes cannot be seen unless the viewer has a reference print for comparison. A fade of cyan dye in a portrait may not be seen easily, but in a forest scene will stand out right off. Fade of yellow or magenta will stand out in portraits but might not be seen easily in a forest scene.
Therefore, due to all of this, I would have to say that no test can be exact or definitive, but merely used as guidelines. Even there they may be way off due to the nature of the tests and the judgments made in defining these guidelines.
The ANSI tests allow for enough leeway to provide no real answer due to the fact that accelerated tests cannot be projected easily back to real keeping.
I think that this, coupled with my last post on the subject may be more than you ever wanted to hear on this.
an interesting read, never enough good info on this subject matter so keep it coming.
I had a thought in the meantime that relates to my work.
Imagine someone using 50,000 FC to fade a print and they find that the print is bad in one year.
They then divide that by 100 to come up with the figure of 500 FC for 200 years assuming 50% daylight per day. So, they say that a print will endure for 200 years.
Here are the problems:
1. The real day / night cycle changes this value. It isn't 50:50 and it involves sunset/sunrise.
2. Lower intensity changes the oxygen saturation and airborne diffusion values.
3. Humidity and temperature changes this.
4. The projection back down to ambient is not simply a division in any case. It is a complex and unknown (and sometimes unknowable) polynomial.
Then, the bottom line, who decides when the print is bad, and what are the criteria.
So this reduces all of the above to a simpler statement.
I have most of the output devices in house, to make cibas, RA4, inkjet ,
What would be a real world test to see the effect of image fade??
I can face mount each print to plexi and mount to a wall outside and or inside that recieves nothing but North Light or just mount them to card and put them into the north facing window.* I did this about 6 years ago and the cibas I mounted are now completely faded, I did not put any media up against this.
Do you think putting them outside face to plexi with a wrap to stop any wetness from behind, is a good test .
I am dying to see the cannon inks vs the epson, ra4 colour against ciba chrome.
I have a cibachrome in my lab that looks as fresh as the day it was made, about 14years ago and I do not want to wait that long to see the results of hanging in just normal room light.
Try 100 fc and 500 fc for about 5000 hours and 1000 hours respectively backed up by 5000 hours north window exposure. These work out to the same in FCH but the last one factors in day/night cycles.
For heat and humidity use about 140 deg F and 70% rh and 120 / 10 for these. If you want to get fancy you can raise the pressure, pump in ozone, sulfur dioxide and etc, or you can try hydrogen sulfide. There are lots of fancy things. There are many many more humidity/temperature variations, but this will suffice.
What you want to look at are neutrals and separation exposures, as they behave differently. Neutrals protect dyes more than individual pure colors do.
You see what a huge experiement we are talking about?
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Thanks for the clarity on this Ron. Personally, I've always distruted Wilhelm, and this shows that longevity of color images is a complex equation.
With inkjet, at high temps and humidity, image spread (sharpness change) is very important. So a comparison of definition charts with Ciba, RA4 and Inkjet are warranted at 140/70.
When I get a bottle of pills from a pharmacy...there is often a little capsule inside to help protect the medicine..I assume it absorbs moisture...
When I buy beef jerky there's a small foil envelope "to preserve freshness" that apparently absorbs oxygen
would it make sense to have something similar for print storage/framing to help protect against atmospheric pollutants?
The little packet works until you open the main package. How would you suggest it work on an open frame or prints being stored? Any ideas? How would it protect against light?
PE Not more than I ever wanted to hear. I picked up more in this concise one page thread than I previously would have thought possible for a layman. Many thanks