How to stretch watercolor paper

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Stretching watercolor paper is an optional step that some watercolorists do to avoid buckling or uneven paint absorption. You can choose to not stretch your paper if you are using: heavy paper (heavier than 140 lb / 300 gsm), pre-stretched paper, or watercolor boards. Even if you're not using any of those supplies, you can still choose to not stretch your paper. At the end of this article, I'll talk about how to flatten your buckled paper if you didn't stretch it beforehand.

Stretching paper is a useful step and you may enjoy it, but some artists choose to skip it. In the end, it's up to you.

Why do artists stretch their watercolor paper?

Stretching watercolor paper does two things simultaneously: 1. your paper will not buckle when you're painting. Buckling can cause your paint and water to pool, making it harder to get solid areas of color. 2. it dissolves the sizing that manufactures add to the watercolor paper to control how absorbent and strong the paper is. The more sizing, the less water the paper absorbs right away, the longer your paint stays wet, the more time you have to play with the paint before it's absorbed into the paper. Sometimes sizing can be applied unevenly which can lead to inconsistent paint absorption. The goal when stretching is not to get rid of sizing completely, but instead to dissolve these unintentional spots of heavily-applied sizing.

If you don't plan on using a lot of water while you paint (for example a dry brush technique), you may not need to stretch your paper.

The paper was not stretched beforehand and it is not buckling since not much water was used.

Supplies needed:

Sturdy support board: wood, foam board, plexiglass, clipboard, glass, etc. Your board should be at least 1 inch larger than your paper and be sturdy enough to resist warping / bending when wet. It also needs to be sealed so it doesn't absorb water from your wet paper.
Tub of cold or room temperature water
Sponge
Watercolor paper (140 lb / 300 gsm or less)
Water-activated gummed tape, staples, or clips
Gloves for handling wet paper

Before you start:

The weight of your paper will determine how long it should be soaked in water. Thinner paper can soak up to 4 minutes, thicker paper can be soaked up to 8 minutes. You'll know your paper is properly soaked when it begins to go limp and behaves like cloth. Remember that heavy weight paper (300lb or 640 gsm) doesn't need to be stretched.

Avoid touching your paper while its soaking for two reasons: 1. the oils in your hands can leave fingerprints that could show up on your final painting; consider wearing gloves to avoid transferring oils. 2. the paper becomes fragile when wet. The more you handle it, the more likely it is to rip.

The method for attaching the paper to the support board varies based on the type of board and intended painting techniques. For instance, with a plexiglass support and plans for wet-on-wet techniques, wetting both sides of the paper can make it adhere to the plexiglass and it will stay on the surface as long as the paper is wet. A wooden support board typically calls for staples and/or gummed tape, while foam or clip boards typically use clips and/or gummed tape.

I've seen some artists use a support board that is smaller than their watercolor painting - similar to stretching a canvas on stretched bars. What they'll do is soak the paper, then fold all four sides of the watercolor paper around the edges of the support board and clip or staple the paper to the board. This allows the paper to become taut when dry and keeps a white border. However, it does crease the paper, so if you plan on removing the paper from the support, just keep that in mind. Or you can iron your paper (I talk about it at the end of the article) to flatten any creases.

The type of tape you use matters - regular masking tape or artist's tape will either not stick to the wet paper or will not stay on the paper as the paper shrinks from water evaporation. Gummed tape is water-activated tape that stretches with the paper. Keep in mind, gummed tape will not peel off your paper; you will need to cut your painting out when done. Ripping the gummed tape off will rip your paper. If you want a border around your painting, add artist tape or masking tape around your watercolor paper after your paper is dry from stretching and before you start your painting.

How to stretch your watercolor paper:

Fill your tub or bucket with room temperature water.
Submerge your watercolor paper completely in the water. Let it soak for a few minutes until the paper fibers are saturated and pliable.
Gently lift the soaked paper from the water, allowing excess water to drip off.
Place the wet paper carefully onto the flat support board, ensuring it's positioned evenly and without any wrinkles or folds. Using a sponge can help.
If using staples, clips, or gummed tape, secure the edges of the wet paper firmly to the board, ensuring the paper stays taut and flat.
Lay your board flat to dry to avoid water pooling at the bottom of your paper.
Allow the paper to dry completely. Avoid moving the board or disturbing the paper until it's fully dry, as this could cause warping or uneven stretching.

Once the paper is dry and firmly stretched on the support board, it'll be ready for paint. There are plenty of ways to prepare your watercolor paper - each artist has their own preference. Experiment and try different approaches to see what you enjoy.

How to flatten buckled watercolor paper:

There are two ways to flatten a buckled watercolor painting: either with weight or heat. Both of these processes should be done when you're finished with your painting and it's completely dry.

Flip your watercolor painting so the back is facing up.
Lightly spray the back with water. Be careful not to saturate your paper because if the water seeps to the other side, it can reactivate your watercolors and cause them to bleed.
Put a dry cloth over the damp paper
Flattening with weight: place a heavy book on top and allow it to dry for a few hours.
Flattening with heat: turn your iron on low and work in circles, never staying in one place for too long. You can burn your paper with this method, so constant motion is necessary.

It may seem like a lot but it's actually pretty simple and will feel very satisfying at the end! Plus it is worth it because watercolor is such a beautiful medium.