Can Watercolour Paper Deteriorate?

If you've pulled out a beloved pad or big sheet of watercolour paper only to find it's soaking up paint like a sponge, don't panic. You're not alone, and it's probably fixable.

Watercolour paper, whether cheap or expensive, cotton or cellulose, can deteriorate over time. There are two main culprits worth knowing about.

1. The first is chemical and/or biological damage. Acids from household cleaners, food smells, vinegar, even alcohol can drift through the air and quietly degrade your paper. Moisture give the opportunity for mould or algae, attracts insects or animals to stop by and snack. You'll usually notice yellowing, dark patches, tears, crumbling or even holes. Unfortunately, this kind of damage is pretty much permanent. there's not much you can do to rescue it. If this is effecting existing art work, especially if its precious, don’t attempt to fix it yourself seek out professional conservators. There are ways to improve the storage and display that can halt further deterioration.
2. The second culprit, the more common one, is the sizing breakdown. Sizing is the term used in paper making circles that refers to any substance added to or applied to the surface to reduce the absorbency of water. Most quality watercolour paper is coated with gelatine, the same stuff that makes jelly set. It's brilliant for painting because it holds moisture and pigment at the surface rather than letting them bleed deep into the paper. The problem is that gelatin is sensitive to humidity, temperature fluctuations, and light exposure. Humid environments or climates are particular culprits, but even leaving your pad on the back seat of a hot car can cause it to fail in patches. The result? Your paper suddenly behaves like blotting paper.

The good news is there are ways to bring sizing back. The simplest fix for the more expensive papers that will have both internal and external sizing is to wet the entire sheet, let it dry completely, and paint on it straight away. You can add the desired level you require in that new painting session. It sounds almost too easy, but it genuinely works, there are plenty of experienced painters who swear by it. The catch is you really only get one go at this, so time it well.

If that's not enough, you can re-size the surface entirely. Powdered gelatine is one option, though it's a bit fiddly. A more practical route is using a commercial watercolour ground.

I have found acrylic gesso also works well. Thin coats work best, I aim for two light layers, keeping the water content below about 30% to avoid bubbling and poor coverage. The dilution allows better flow/coverage and also gives you control over absorbency. More water leads to more absorbency, so a bit of experimentation and you can get back to something close to the original paper feel.

One tip worth trying: instead of a brush, use a small foam roller to apply the gesso. It leaves a fine, even texture similar to cold-press papers that's genuinely lovely to paint on. Especially if you're working with granulating pigments that like to settle into small dips and hollows.

So before you throw out that dodgy paper, give it a second chance. Chances are, it's not as far gone as it looks.