Fade test

[JBrunner]

OK, I'm running a decidedly non scientific test- A light fade test to be specific. Basically I've cut a print in half, stored one half in a dark place and taped the other half up in a south facing window behind glass that is old and nothing special, where it gets direct sun all day. I'm doing this because it is a rather off beat process that I have twisted further, and I'd like to know it is light stable.

My question is taking the season and my mid northern latitude, roughly how much time in direct sun correlates how much time under normal display conditions? There's nine stops of difference of visible light, I wonder does UV follow that same ratio?

 

[Photo Engineer]

For B&W this might take a long time, years in fact.

For recent color materials it might take the same long time.

I would say though that 2000 - 4000 hours of true daylight should show some difference if there is going to be any change and this should be worth about 10+ years of display. The change may be very small and may require a densitometer to actually "see" it. BTW, that 2000 hours is a long time. It is nearly 1 year. And, winter is more severe than summer in north latitudes if you just count daylight hours. This is because there are no shading trees or plants to block sunlight and the angle is such that it comes in the window more directly.

UV is an important factor. If your window filters out UV, then the test will be biased. If the window is cold and the print is close enough to "feel" the cold, then the test will be biased. Indoor humidity is low in winter and high in summer, and this will bias the test. Pollutants in the air will bias the test, so cooking odors, nearby factories and etc are factors in this evaluation.

Have fun.

PE

 

[Martin Aislabie]

PE - is there anything much that doesn't influence the rate of fade?

So far from your post I have :-

Direction the Window faces

Poximity to the window

Temperature

Humidity

Atmosheric Polutants - both local to the print and for the surounding area

UV Levels

Latitude

Thanks

Martin

 

[Mike1234]

"Ordinary window glass passes about 90% of the (UV) light above 350 nm, but blocks over 90% of the (UV) light below 300 nm."

From: http://en.wikipedia.org/wiki/Ultraviolet

 

[Photo Engineer]

Some people have special UV blocking window glass. So.......

Martin;

Hours of daylight count (Latitude + time of year). Snow reflects more light than bare ground. Pollutants must be factored in by type such as SO2, H2S, O3 and etc. Altitude has an influence by decreasing O2 partial pressure on the photo but increasing UV.

Now to go on, the film or paper are also factors with things such as gelatin thickness, gelatin addenda, UV absorbing layers, Oxygen barrier layers, Free radical chain stoppers (color) and others added. In addition we have to consider contaminants in wash water.

That is why the tests are usually run with a daylight simulating light source under controlled atmospheric conditions with side experiments with temperature, humidity and pollutants in special "ovens".

Usually 5 tests are run.

1. The real thing using daylight.
2. A simulated daylight which is on 24 hours / day and which is at a high intensity.
3. A wet oven with high humidity and temp.
4. A dry oven with low humidity and high temp
5. A mixed pollutant atmosphere at high temp and may have high or low humidity.

With color, there are 2 types of these tests. One is done with neutral scales and the other is done with color scales. Color scales fade differently than they do in neutral scales.

A wide strip is read stepwise across each step to verify uniformity and is then split into 6 parts. One part is placed in a dark cold storage container and the other 5 are sent for the above tests. They are removed periodically for remeasurement and then returned to the test area with careful handling in between. The change in density and dmin are plotted as a function of time. Usually, density decreases and dmin increases. At the end of a given interval, an Arrhenius calculation can be done to estimate the true life of the photo.

PE

 

[JBrunner]

Just to clarify, this is a toned cyanotype, bleached first with an alkali, and then developed back in tannic acid. The bleaching isn't severe, so my thought is that there is Prussian Blue left in the dark areas. I've read that the alkali converts the Prussian Blue into ferric hydroxide, which is unstable. I'm curious if the tannic acid locks the ferric hydroxide back up into a ferrotannic, something that should hang around for a while.

It's been in the window for ten days. During the first five there was a barely perceptible loss of Dmax, and nothing changed in the mid tones or highlights. Since then there has been no change. I'm theorizing that there was initially some reaction/oxidation due to an impurity or perhaps some unconverted ferric hydroxide, but that stability was achieved after the impurity "burnt up". Time will tell. I will also be curious to see if returning the sunlit part of the print to darkness for a while will return the Dmax, in which case the fading may be the normal and documented behavior of some residual (unconverted) Prussian blue compounds, which would be living in the darkest areas of the print, if they are still there.

 

[Photo Engineer]

Jason;

Ferric and Ferrous Hydroxides are very stable from my experience. They are common retained contaminants from Blixes and Bleaches using Ferric EDTA. They are classed as pigments. (or rust --- )

PE

 

[Martin Aislabie]

Some people have special UV blocking window glass. So.......

Martin;

Hours of daylight count (Latitude + time of year). Snow reflects more light than bare ground. Pollutants must be factored in by type such as SO2, H2S, O3 and etc. Altitude has an influence by decreasing O2 partial pressure on the photo but increasing UV.

Now to go on, the film or paper are also factors with things such as gelatin thickness, gelatin addenda, UV absorbing layers, Oxygen barrier layers, Free radical chain stoppers (color) and others added. In addition we have to consider contaminants in wash water.

That is why the tests are usually run with a daylight simulating light source under controlled atmospheric conditions with side experiments with temperature, humidity and pollutants in special "ovens".

Usually 5 tests are run.

1. The real thing using daylight.
2. A simulated daylight which is on 24 hours / day and which is at a high intensity.
3. A wet oven with high humidity and temp.
4. A dry oven with low humidity and high temp
5. A mixed pollutant atmosphere at high temp and may have high or low humidity.

With color, there are 2 types of these tests. One is done with neutral scales and the other is done with color scales. Color scales fade differently than they do in neutral scales.

A wide strip is read stepwise across each step to verify uniformity and is then split into 6 parts. One part is placed in a dark cold storage container and the other 5 are sent for the above tests. They are removed periodically for remeasurement and then returned to the test area with careful handling in between. The change in density and dmin are plotted as a function of time. Usually, density decreases and dmin increases. At the end of a given interval, an Arrhenius calculation can be done to estimate the true life of the photo.

PE

Thanks PE

Pretty simple, straight forward testing

Martin

 

[JBrunner]

Because I'm a curious sort, I cut off part of the print that is in the window and washed it. Dmax has been restored. The piece now again matches the part that has been dark stored. I'm not sure what this means.

 

[Ektagraphic]

Actually, this is a little off topic...especially for the B&W forum but I did this with some Kodachrome slides that I didn't want and nothing happened. Interesting results......

 

[JBrunner]

Actually, this is a little off topic...especially for the B&W forum but I did this with some Kodachrome slides that I didn't want and nothing happened. Interesting results......

Cyanotype has a long history of rather strange behaviors, regular cyanotypes that have faded can often be "reversed" to some degree by dark storage, etc.

You can re-wash conventional films and prints but generally the only change is they will just be cleaner. I wouldn't re-wash an RC print maybe. IDK. I've rewashed film for various reasons many times.