formaldehyde use in glue painting

[rick2009]

Greetings,

A. Some artists who use glue painting will spray a coat of alum/glue/water on a painting when the pigments, upon drying, have become powdery and lack adhesion due to too much water and not enough glue.

Can formaldehyde be used to remedy lack of adhesion of a paint layer ( due to a watery mixture with insufficient glue content ) ?
If so, how? By spraying it on as is from the bottle or mixing it with a glue water solution ?

B. Alum is used in the glue/water mix as a coating, functioning as a sealant and primer I believe, to prepare watercolor papers for glue painting.

Can formaldehyde replace the alum for this purpose ? Again, if this is possible, how should it be done ?


All of the best,

[George O'Hanlon]

Some artists who use glue painting will spray a coat of alum/glue/water on a painting when the pigments, upon drying, have become powdery and lack adhesion due to too much water and not enough glue. Can formaldehyde be used to remedy lack of adhesion of a paint layer (due to a watery mixture with insufficient glue content)?

No, spraying a solution of formaldehyde or aluminum sulfate over a layer that does not have enough glue will not remedy the problem. You need to add more glue solution to the paint layer.

Alum is used in the glue/water mix as a coating, functioning as a sealant and primer I believe, to prepare watercolor papers for glue painting. Can formaldehyde replace the alum for this purpose? Again, if this is possible, how should it be done?

That is incorrect. Aluminum sulfate and formaldehyde do not function as a primer or sealant (which are entirely two different functions). Formaldehyde, for example, cross links protein molecules in collagen, hardening the glue thereby making it less reactive to moisture. There are several substances that have similar reactions with collagen, such as aluminum sulfate, chromium(III) potassium sulfate and chromium(III) sulfate. This is in effect the same reaction that takes place when tanning animal skins to form leather.

[rick2009]

Thank you for replying.

In both cases, either to seal paper... or to correct improper adhesion...the alum is added to the glue solution.... then applied. Sorry if I was not clear about that.

If I wanted to use the formaldehyde instead of the alum.. for either of these applications...how would I do that ?

I am thinking that the formaldahyde would need to be added to the glue solution in some way. Would it not ? Or could it be sprayed on before or afterwards ?

Perhaps right afterwards while the glue solution is still moist so it would integrate with the glue solution?

All of the best,

[George O'Hanlon]

In both cases, either to seal paper... or to correct improper adhesion... the alum is added to the glue solution.... then applied. Sorry if I was not clear about that. If I wanted to use the formaldehyde instead of the alum... for either of these applications...how would I do that? I am thinking that the formaldehyde would need to be added to the glue solution in some way. Would it not? Or could it be sprayed on before or afterwards? Perhaps right afterwards while the glue solution is still moist so it would integrate with the glue solution?

In either case, aluminum sulfate (alum), formaldehyde or any other fixative substance will not create a "seal" or remedy "improper adhesion" of the pigment in the paint film. It simply hardens the glue, making it less susceptible to moisture, but it does not make it impervious to moisture. You can add the fixative substance to the glue solution or spray it onto the paint film. Adding it to the glue solution is the better of the two methods of accomplishing this.

[rick2009]

Thank you for replying.

I am considering making a weak solution of alum that I can add to the glue solution for all paint layers including the gesso layers.

Will this solution (of dissolved alum) keep for a couple of weeks or should I use a fresh solution more often ?

I am also considering using formaldehyde as a final step in the painting process after all the layers have been added. (As opposed to adding it to each layer.) This seems to me to get the most out of the formaldehyde as it will be protecting the exposed areas of the work. Does this make sense?

The thought of using hardeners reminds me of the issues that can occur with oil paint dryers. I would imagine that, ideally, hardeners in glue solution should be used equally throughout the work so that equal tension is somewhat maintained ? If random layers were hardened this might cause weakness in the layers and possibly cracking and/or other issues under certain conditions ?

PS: Can the use of alum cause cracking ? Would too much formaldehyde cause cracking ? If I have a little alum in my paint layers will the use of formaldehyde as a final step still be advisable ?

[George O'Hanlon]

I am considering making a weak solution of alum that I can add to the glue solution for all paint layers including the gesso layers. Will this solution (of dissolved alum) keep for a couple of weeks or should I use a fresh solution more often?

Yes, the solution will keep indefinitely.

I am also considering using formaldehyde as a final step in the painting process after all the layers have been added. (As opposed to adding it to each layer.) This seems to me to get the most out of the formaldehyde as it will be protecting the exposed areas of the work. Does this make sense?

We recommend either using the aluminum sulfate or the formaldehyde, but not both. Also, it appears to us that you may be overthinking the process of glue painting. We recommend keeping the process as simple as possible, such as adding a weak alum solution to the painting or none at all. See my further comment below.

The thought of using hardeners reminds me of the issues that can occur with oil paint dryers. I would imagine that, ideally, hardeners in glue solution should be used equally throughout the work so that equal tension is somewhat maintained? If random layers were hardened this might cause weakness in the layers and possibly cracking and/or other issues under certain conditions? Can the use of alum cause cracking? Would too much formaldehyde cause cracking? If I have a little alum in my paint layers will the use of formaldehyde as a final step still be advisable?

The issues for oil painting and glue painting are quite different. You are correct that hardeners ideally should be used uniformly throughout the paint film, but in practice this may be difficult to achieve. It is possible that the use of aluminum sulfate or other hardeners and fixatives may lead to cracking, if not used correctly. There is not much information or research to show what the final outcome of the use of hardeners in glue paintings may be, so we recommend testing first. In any case, the best practice to avoid cracking of the paint film is to paint on rigid substrates. The use of flexible substrates is perhaps the leading cause of paint film cracking and delaminating. Also, protect the painting from rapid changes in humidity by applying a moisture barrier on the reverse side of the painting and, although less desirable, cover the final painting with a picture varnish or picture glass. Taking these simple precautions will do more to help avoid cracking of the paint film and eliminate the uncertainty of using hardeners in your paint.