Chemical Interactions with Stains Applied to Photos

      Here's a complex discussion of the possible chemical reactions that could cause wood stains to change color properties when applied to old black-and-white photographs as part of a custom art work. July 18, 2008

Question
I am having a problem with some colored wood stains that are fading completely once applied. I am an artist who uses wood stains to add color to traditional black and white photographs and constructed wood sculptures.

I recently purchased some oil soluble powders (Red, Scarlet, Green, Blue, and Yellow) from WD Lockwood and mixed them as directed. (1oz. powder dissolved in 1pt. lacquer thinner.) I then added the dissolved concentrate solution to different oil based clear finishes and tested them on some photographs. The concentrated mixtures are stored in plastic containers while the diluted (concentrate mixed with oil stain) are stored in pint -sized metal paint cans.

I tested the colors in the following finishes:
Varathane Wiping stain
Old Master Gel Stain
Old Master Tung Oil
and Minwax Natural.

Two days later, I found that the blue, green and yellow stains had all but faded completely on the photographs. Within four days, all color was gone and only the residue of the finish was left behind. Even the rags I used to apply the stains had faded badly.
I have used colored oil based stains before on my photographs and sculptures and have never had this problem. WD Lockwood has been around for a long time so I'm pretty sure they are not selling inferior product. This is the first time I have mixed the stains myself and am wondering what I may be doing wrong. My shop has no direct sunlight exposure, lit by 5000k fluorescent, is normal room temperature, and there are no noticeable fumes present. Yet it seems to me that some chemical reaction is taking place.

The only variation between the stains that faded (blue, yellow, green) and the ones that did not (red, scarlet) is that I used new lacquer thinner for the colors that did not fade. But then I ran out and found some very old lacquer thinner (4 years) to dissolve the ones that eventually faded. Other than that, the mixing ratio and method was the same for all of them.

Is it possible that old lacquer thinner can be the culprit? Does lacquer thinner change over time? Would lacquer thinner even be the problem? Should I try a different solvent besides lacquer thinner? Any help would be appreciated.

Forum Responses
(Finishing Forum)
From contributor M:
If I read you correctly, sounds to me that there is a color reaction that is happening with a chemical on the photograph that is used in the development process. I know for a fact that the old "photographer's hypo" chemical used in development will absolutely neutralize chlorine. A lot of fish keepers in the days gone by would purchase photographer's hypo to use as a tap water decholorinator, and a touch went a very, very long way. It sounds to me that residual chemical on the photos is killing you. Try using your process on something inert like a piece of Plexiglas or lexan and see what happens.



From contributor M:
You'd be shocked at how little hypo is needed to dechlorinate a large amount of water. Make sure to run your color process over something other than the photographs. Try to replicate your entire procedure to see if the problem is only duplicable on the photographs. If it only happens on photographs, then the fading problems are originating almost certainly from some sort of reaction with the photograph.


From the original questioner:
Seeing as how this is my first time doing this, I figured it would be operator error. Seeing as how I have done this before using pre mixed stains, I am going to try mixing some new stains and store the mixture in plastic. Do you think the 1 pint containers form the paint store will work?


From contributor C:
Any polyethylene plastic will work well.


From contributor R:
I tried Lockwood’s oil dyes and was not impressed. They were not very light fast and liked to bleed. I would go with an NGR stain. Mohawk, Sherwin Williams, Valspar, Chemcraft , MLC and probably every large coatings manufacturer has them.

As far as the photos oil colors are the traditional method for coloring black and white prints. Marshalls makes oil colors for this purpose and oil pencils also. As an artist you may be experimenting with some new techniques and that is cool also. Let us know what you find out.



From the original questioner:
I tried Marshalls once but my work is so large scale (3x4 ft) that it was just too expensive. I use wood stains because they are much more fluid and I can experiment a lot more.

But taking a cue from you, I will search the forums for more opinions on what may be the better dyes and pigments. I simply went with Lockwood’s because that’s what popped up when I looked on the web. But their instructions do not seem to be consistent when you compare the web version to the instructions that come written on the packet and even those are different from the separate paper that comes with the shipment. Nor are their web prices current. That's the reason I dissolved the powders in LT because the written paper that came with my shipment said to do so.



From contributor R:
Lockwood water based dyes are very good but I don't think they will work for the photos however they will work great on the wood.


From the original questioner:
Another thing about my artwork is that once I have applied the stain to my photographs and allowed it to dry; I then apply a thick coat of epoxy resin over the whole thing.

My question is, would the light fastness of the pigment change (increase) due to the resin sealing it all? Can fading still occur even if the pigment lies under a coat of impermeable plastic and is not exposed to the atmosphere?



From the original questioner:
Is there any kind of light-fastness standard rating system I can reference when shopping around for pigments? Kind of like the ISO film ratings we have in photography?


From contributor C:
You have many more things to look at than just pigments/dyes. First, in time your epoxies are going to yellow, depending on what the makeup of the one you’re using is. It could be slight to drastic. I doubt you’re using a conservation epoxy that has shown itself to yellow little over a long period, so I'm presuming it's a store brand. The only coatings you can use that will not yellow that are readily available to you are:

acrylic coatings
vinyl copolymer coatings
cellulose acetate
butyrates
or there copolymer - CAB

Second - there is so much potential for solvent/coating reaction with what you’re doing and possible adhesion and other ramifications. If I were you I would (and have done) study the chemistry of photography, the same with coatings, and with solvents and dyes, as to where and how they can be used together in harmony without causing potential problems. Now that i know you’re using epoxy over an already iffy system it's even more difficult to say what your long term results are going to be. Personally I feel they don't look good.

As to color fading scale look up blue wool scale on the internet this is used by the dye manufacturer to determine the fade resistance for dyes and dye types.



From the original questioner:
Yes! That's what I've been looking for - the blue wool scale. I have been using the epoxy coatings for about four years now. I have done a lot of research and found one that performs well. It adheres great, yellows very little, and is pretty inert once cured.

I've come to the understanding that nearly all epoxies yellow over time and the one I use now is from an industrial manufacturer in California. So, I actually factor in the yellowing when I'm choosing colors and I then "season" the piece with a little sunlight before sending it to market. I also let my patrons know that the piece is not to be exposed to direct sunlight, which is common practice with fine art anyway. So fortunately, there have been no issues.

I would be interested in knowing, however, if any of the alternatives you cited: (acrylic coatings, vinyl copolymer coatings, cellulose acetate, butyrates or there copolymer - CAB) are available in a high viscosity form? (Think thick table top coatings or surfboards).

That's the key for me as I have found store-bought acrylic to be far too thin for the effect I'm seeking. If there is a better non-yellowing, yet super thick finish I can use, I would love to know about it.



From contributor C:
There are acrylates called B-72 in solid form and then let down in the vehicle of your choice. The problem is there only soluble in polar solvents so this may raise a problem. Talk to them to make sure first.

I know from use you can make a very thick solution of the product but there will still be shrinkage and the solvent selection will have to be one that does not affect the photo chemicals. Epoxy is not a bad choice as long as you know it will give you long term performance. It sounds like you've already done testing so if you’re happy with the results stick with it.



From contributor A:
Acryloid B-72 (referred to as Paraloid B-72 in Europe) is a thermoplastic acrylic resin manufactured by Rohm and Haas, which has replaced PVA in many applications and is preferred by many conservators over PVA. It is a methyl acrylate/ethyl methacrylate copolymer and is an excellent general-purpose resin.

Durable and non-yellowing, Acryloid B-72 dries to a clear transparency, with less gloss than PVA, and is resistant to discoloration even at high temperatures. It is very durable and has excellent resistance to water, alcohol, alkalis, acid, mineral oil, vegetable oils, and grease, and it retains excellent flexibility. Acryloid B-72 can be applied in either clear or pigmented coatings by a variety of application methods and can be air dried or baked. It has a very low reactivity with sensitive pigments. Furthermore, it is compatible with other film-forming materials, such as PVA and cellulose nitrate, and can be used in combination with them to produce stable, transparent coatings with a wide variety of characteristics. In stronger concentrations, Acryloid B-72 can be used as a glue, consolidant, barrier coat or full coating.

Acryloid B-72 is unique in possessing a high tolerance for ethanol, e.g., after being dissolved in acetone or toluene, up to 40 percent ethanol can be added to the solution to control the working time. This property allows its use in applications where strong solvents cannot be tolerated. The alcohol dispersion may be cloudy or milky; however, clear, coherent films are formed upon drying. Friable surfaces of porous, salt-contaminated objects can be stabilized with Acryloid B-72 while the salts are being diffused out in water baths without the adverse effects resulting from the use of soluble nylon.

Krylon Clear Acrylic 1301 is a formulation of 20 percent Acryloid B-66 in non-water miscible toluene that is easily obtained and is excellent for consolidating or sealing off the surfaces of a wide range of material. It is a ethyl methacrylate resin that is harder than Acryloid B-72 and can be used in place of it in most instances. I buy B-72 in 100% solids form so that I have full freedom of solvent choice and percentage.



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