Monday, March 14, 2011

Watercolor Woes. Troubleshooting Paper Discoloration

Ever find yourself wondering why your watercolor painting done a year or so ago has started yellowing or browning despite you making sure you used acid-free paper?  Chances are, you may be unknowingly doing something that is putting your art at risk for early deterioration.  

Acidity is only one factor among many that may cause early damage to your painting.  But if you can eliminate acidity as a potential problem, it will be a big contribution to the long term preservation of your painting.  What exactly does acid do?  Acid can cause premature breakdown of materials in paper, canvas and wood.  It may also degrade your pigments, specially the paints that contain elements of metal in them.  

When you buy your acid-free watercolor paper from the manufacturers and suppliers, it is as they claim, in a state of being free of acid.  The paper has been processed so that naturally occurring acids and acids used in the processing of the paper pulp are neutralized and thus made harmless.  However, this claim is not a guarantee that the paper will be immune from whatever treatment you are bound to subject it to.  The responsibility of keeping your watercolor paper acid free is yours, once you get your hands on the paper.  

How do you get acid on  your paper?  By getting chemicals on it that change the pH of your paper and by putting it into direct contact with materials that may leech acid.  

Some advice the use of distilled water for your watercolors, for just this reason.  A bit extreme and expensive.  I, myself, only use the distilled water for the water mister I use to wet my palette (distilled water prevents the water in the bottle from getting mossy).  But the use of distilled water for wetting may be the best solution for those who get their water from untested sources.  E.g.  Some ground pumps produce discolored and metallic hinting water which could not only stain your paper but also might turn out to be acidic.  
Another source is the use of bleach to whiten or erase a mistake.  You may even read of instances where people (most likely students and not professional artists) immerse whole papers in it to bleach out color on an already used watercolor paper.  Technically speaking, most bleaches are strong bases (very high pH).  But strong bases have the same degrading qualities as acids.  You are still messing with the pH of your paper.  
One popular technique for achieving beautiful textures in watercolors uses salt.  I've seen wonderful works of artists using this technique. Done right, you will not even be aware, salt has been used.  I'm tempted to try it myself but the use of it is quite controversial so I'm holding out.  Lately it has been claimed that salt is actually acidic or causes the paper to be acidic.  Who would have thought, eh?  But as that is still under contention, it probably is best that we wait for the official findings before we put a final verdict on its use.  Meanwhile, I'm experimenting on safer alternatives.  If ever I turn out a closely similar effect using very neutral materials, I will share on the blog.  

The most common cause of getting acid on your paper though is by the use of unprotected wooden boards for stretching.  Most beginners do not realize that the reason wooden boards sold in art workshops and art stores are expensive is because these have undergone more labor intensive treatment than your regular boards.  These stretcher boards have been sanded, primed and sealed several times to make the surface as non-porous as possible.  These are made to withstand getting wet paper on them.  Students and beginners often improvise on a lot of things in an effort to save money and the drafting board is often used as a replacement stretcher board.  They surmise, both boards look similar anyway.  But most drafting boards are just something a little better than bare plywood.  Most often, their manufacturers only sand the surface to give the students a smooth surface to do their drafting on.  They were not intended to get wet.  Now what does unprepared wooden boards have to do with acidity?  Just this.  Even with oven dried / sun dried wooden boards, the moment you wet the wood fibers (as what would happen when the wet paper gets in contact with the dry board), you start reconstituting the dried acid in the wood with water.  Think tea.  As your paper dries, it would pull the now acidic water from the wood onto the back of your watercolor paper.  The damage can sometimes be readily obvious and you're lucky if you spot this right away.  It would save you the effort of painting on damaged paper.  But sometimes, the damage may become apparent only after weeks, months, or years. By then, too late.  More than the loss of paint and paper, I think I would be sorrier for the time invested in a painting that would get ruined earlier this way.

Protect your art, use a safe stretching board or use paper that require no stretching.

On my next post, I will upload a simple yet very affordable solution that would help make your untreated/unprotected wooden supports, waterproof.  This is for fellow watercolorists, specially in my country, who have no access yet to gator boards.  (The only way you can get gator board or similar here is through online stores abroad).  I'm still employing this method to waterproof the support for my watercolor paintings, specially the ones that have unusual dimensions that do not fit on the gator boards that I have.

Here's a pic of a watercolor painting that I stretched on a home-made waterproof board (taken years ago).  I like how you can go as big as you like.  Even make a support the size of the whole plywood board 4 x 12 feet.

Other related articles:
Additional protection you can do yourself for your framed watercolor painting
Affordable and easy solution for unprotected wooden boards used for stretching watercolor paper
Stretching guide: understanding watercolor paper weights
Understanding sizing: guide to wetting your paper
Gator boards



  1. I'm so happy I found my way to your blog. Yesterday, I bought some plywood for stretching my paper. Today, my instincts kicked in and I had a bad feeling about it. Even though I payed $20 for some nice wood, it looks like my art has just dodged a bullet! Thank you very much for your article. :)

    1. Wow! As I explore your blog more, I'm finding so many interesting articles. Since you welcome conversation, I'm delighted to thank you again, for everything!

  2. Hi Salina,
    My apologies for the lateness of my reply. I was not getting the notifications for new comments on the blog. Probably because I could not load pages (had several months of bad internet connection). Do not throw away the good wood though. With sealing, you can still use that as a base for your stretching. I have heard of artists successfully sealing boards with several layers of marine sealant. Alas, I will have to find out if this is really the general term for the paste. They sand in between coats to increase adhesion between the layer. I have yet to try it myself. So there is hope yet for your good plywood with sealant. :D