You’ve seen it happen… Right ?
You lay down a nice watery wash of paint, you settle down to enjoy your painting, and then… It all goes lopsided !
When watercolor paper absorbs liquid, it buckles and deforms, leaving ridges and depressions which make paint flow difficult to control. It’s a nuisance which all watercolor artists have to deal with. This is pretty annoying because as you continue to paint, pigment tends to run into the low valleys and settle in pools. Stretching your paper is the common solution.
I used to think that simply by using watercolor paper you could avoid this problem. But even watercolor paper expands when it becomes wet.
Yep… Even though watercolor paper is designed to accept water based medium and is quite stable, it still warps because of wetness. This is especially true if you add a lot of wet watercolor washes or pre-wet the paper for a wet on wet technique.
So how do you avoid this pesky problem ?
Most artists stretch their paper to overcome warping. But I’ve found there are a few different ways to do this. Indeed, some watercolor artists invent ingenious ways to prepare their paper. Each method has its own advantages and drawbacks.
So I thought I’d put together this article to show you 3 different ways for stretching your paper and 1 common example of how NOT to stretch watercolor paper. Plus as a bonus, I’ll even suggest how you can avoid stretching paper altogether !
Why do you have to stretch watercolor paper?
Primarily we stretch watercolor paper to avoid “cockling”. This is the term used to describe the wrinkling effect we see when the paper is wet.
Good quality watercolor paper is made from 100% cotton fibers. The method used to manufacture commercial paper causes the paper fibers to align in the same direction.
When the paper fibers absorb water they expand lengthwise, and they take on a more random alignment. When the paper dries, the fibers contract again. But to some extent the fibers retain their irregular alignment. This change in the structure of the fibers is what causes raised ridges and low valleys to form on the surface of the paper which we see as buckling.
(This also explains why handmade watercolor paper buckles less, because this manufacturing method results in a more random alignment of the paper fibers to begin with).
So stretching is designed to eliminate the problem of cockling.
But there’s also another interesting and useful consequence of paper stretching.
Commercial watercolor paper is also treated to alter its absorbency and improve its handling. This is done by adding a chemical known as sizing.
Untreated paper is like blotting paper and has a very high rate of absorption. Sizing is designed to help control this characteristic so that all of your paint doesn’t get sucked up by the paper !
But sometimes watercolor paper can have irregularities in the surface sizing.
If the absorbency of the surface is not regular this can cause blotches when you apply a wash of color.
The methods used to stretch paper help to dissolve some of the sizing, creating a better distribution of sizing across the paper and a more receptive surface.
Dissolving the sizing is an incidental result of soaking the paper during the stretching process, but it's also common for some artists to brush their watercolor paper with clear water before working to eliminate the problem of blotchy sizing.
How to stretch watercolor paper
Whichever method you choose to stretch your paper, the basic approach is the same: first you soak the paper, then you stretch it.
When you soak the paper it expands. You then fix the edges of the paper so that when it dries and contracts the surface is pulled tight like a drum. When you begin a painting session your paper is pre-stretched and it won’t warp or crumple. You now have a perfectly flat surface while you work.
Soaking the paper
You begin by wetting the paper. For this most artists opt for one of the following methods. Soaking with a spray bottle, sponge, or large brush. Or immersing the sheet in a tub of water. Lukewarm water seems to help the paper expand more quickly.
Spraying the paper rather than immersing it takes a little more time.
If your using a sponge or bristle brush, be careful not to wipe over the sheet too firmly, as this will raise the fibers on the surface and can damage the paper.
If you’re soaking in a tub, simply plunge the sheet into your water container. If the sheet doesn’t fit completely, dip one end into the water and drag the paper through the water from one end to another repeatedly.
If you opt for the spray or brush technique, you can place your paper on a clean board, soak it, then turn the paper over and soak again. Repeat the process until the paper is fully soaked.
Personally, I prefer the immersion method because there is less chance that you damage the paper.
How long do you need to soak watercolor paper ?
You need to soak your paper just the right amount of time or you can run into problems later. If you soak too much, the paper expands considerably. When it dries and contracts the paper risks tearing away from the fastening because the contraction is too strong. On the other hand if you don’t soak enough, the paper will dry flat and taut, but when you add watercolor washes it may still buckle.
About 5 to 10 minutes of soaking is usually about all you need. I use Arches watercolor paper most of the time and I find this is sufficient. (Its important to use good quality paper. Arches is one of the best brands. You can read more about my favorite watercolor paper here).
I recommend you do some testing if you use a different brand.
You’ll get a feeling for when to stop soaking the paper, when it turns limp and starts to behave like cloth. The paper loses its springiness when it’s sufficiently dampened. Test the “spring” by folding a corner from time to time to see if the paper is fully soaked.
The thickness of the paper will affect the amount of time needed for soaking a sheet. The average time for soaking with 300 gsm paper is at least 5 minutes. Heavier papers require more soaking time and lighter papers need less time.
Don’t soak too long because you don’t want to dissolve all of the sizing. This treatment is added to improve the performance of the watercolor paper. If you soak too long the internal sizing will wash away.
Stretching the paper
To stretch the paper you need to fasten the soaked sheet to a smooth flat rigid surface. It’s good to use a board which is at least 1” larger on all sides than your sheet of paper. This leaves room for taping the paper to the board.
Lay the soaked paper onto your chosen support and if needed, make sure it’s flat by chasing out any air pockets using a clean sponge. Make sure you put the paper the right way up ! If you’re using single sheets you can tell which is the front side by looking at the watermark. Orient the sheet so that the watermark reads correctly.
The paper will “stick” to the surface when its wet so try to position it correctly the first time, otherwise it can be tricky to move around.
Some good materials to use for stretching boards include:
Marine grade plywood (A good choice if you prefer something solid. Make sure the surface is smooth and consider painting it with an acrylic primer to make the surface less porous. ½” is a good minimum thickness).
Gator foam board (stronger than normal foam board, but still just as light, and with an impermeable surface).
Plexiglass (stable, lightweight and adds the advantage of transparency).
Canvas frame or stretcher bars (lightweight and cheap).
There a different ways to fasten the paper down to the board or frame. The most common is using gummed tape which is easily available. Another popular method is with staples, but I recommend you use a heavy duty stapler.
How long does it take for watercolor paper to dry?
Try to leave the paper in a warm dry place to dry overnight. 24 hours is a good average but you should test the paper to check if it still seems cold or damp before using it.
Some watercolor artists stretch their papers in advance and store them on stretching boards, so they are ready for use.
Make sure you leave the board flat while drying, and not upright. If you stand it vertically, the moisture will run to the bottom and may cause the gummed tape to pull away from the board.
A lot of artists will warn you against using a hairdryer to dry the paper.
In reality this seems to depend on the method you use for stretching, but also how well the paper is fastened down. In general the paper needs to dry at the same rate all over and your paper should not be soaked for too long.
A bit of patience pays off !
4 Ways to prepare watercolor paper:
1 - Completely soak and tape with gummed tape
This is probably the most common method. Here I’m using a marine ply board but you can use gator board with this technique. Just make sure your board is clean and won’t transfer color to the paper and is rigid.
Soak the paper using one of the methods described above.
To fix the soaked paper you need some gummed tape. This kind of tape is water activated. You just need to wipe the glue side of the tape with a wet sponge to activate the glue. Be careful not to wash the glue off by rubbing or wetting too much.
If you’re a perfectionist you can draw some pencil guidelines about a ¼” around the inside edges of your paper. This will help align the gummed tape precisely.
Gummed tape is a better option than masking tape. Gummed tape will stretch with the paper but masking tape will not. Be careful not to drip glue from the gummed tape onto your paper, the glue will dry and cause blotchy marks when you paint.
Tape the paper down on all four sides, starting with two opposite sides. For example left and right, then top and bottom. Check for air bubbles while taping.
This kind of fixing is good most of the time, but to be safe it's a good idea to add some staples to reinforce the fixing. The paper shrinks and tries to pull away from the taped edge. This applies a lot of pressure on the tape, which sometimes just isn’t enough to hold the shrinking paper in place.
Lay the board flat to dry. To remove your painting cut around the edges of the sheet using a sharp craft knife. If you try to remove the gum tape you risk ripping the painting !
If you get the soaking time right, this method is solid and reliable. The downside with marine ply is that the board is heavy, but gator board can be difficult to find if you’re in europe. I often use this method with a sheet of plexiglass. This is extremely useful when you want to use the transparency of the plexiglass to help transfer a drawing onto your watercolor paper. You can put your prepared board onto a light box or up against a window.
2 - Stretching on a canvas frame
I’ve seen a lot of artists use this method which results in a nice tight paper surface. It’s a technique I first learned from the artist Ewa Karpinska.
For this method you need an empty canvas frame or canvas stretcher bars. You can either get hold of some cheap frames and strip the canvas, or buy stretcher bars and make your own frames.
Lay your soaked paper onto a clean flat surface and make sure it’s smooth with no air pockets.
Place the canvas frame in the center of the sheet and wrap the paper around the back edge of the frame.
I recommend you use a heavy duty stapler to fix the paper in place, it just makes the job easier. Start by stapling in the middle of each side, and work your way around. The corners should be folded neatly, and stapled in place.
Leave flat to dry. The final result is beautifully smooth and a pleasure to work on.
You can create all kinds of sizes or customized frames with this method. The frames are very lightweight, and you can even keep it on the frame so long as you protect your watercolor paintings (use something like Renaissance Micro-Crystalline Wax Polish). This method also has some advantages for artists who like wet on wet techniques. Being able to test the wetness of the paper by touching the backside of the paper is a huge benefit !
3 - Using a watercolor paper stretcher
The final method is to use a specially designed paper stretching board. The system was originally invented by the British watercolor artist Ken Bromley. He called it the “perfect paper stretcher”.
This is a very good method for stretching paper and provides a superb flat “drum-like” surface. The board has grooves around the edges. You use rubber strips to secure the soaked paper in place. You may need to use a hammer to force the rubber back in place, which adds a good amount of additional tension. Some artists recommend putting candle wax into the grooves beforehand so that paper removal is easier.
And because the paper is so firmly held in place you can also use a hairdryer to speed up the drying process !
This method is very efficient but pricey. No messy tape to clean up. Not easily available in the US but you can get them shipped from the UK or find them directly at the Ken Bromley Art supplies store.
How NOT to stretch watercolor paper
This is a technique which some artists refer to as quick and easy. The whole process is done directly on the board and with less water, so it’s a bit less messy.
I’ve seen artists show this method and to be honest i had my doubts, so i thought I would test it before passing judgement.
Tape your paper down to a board and use masking tape to fix the paper in place.. Make sure there’s no air trapped under the paper.
Now wet the paper using clear water and a large soft brush. Go over the paper a couple of times to make sure the whole surface is dampened.
Finally dry the paper using a hairdryer !
This method is simple and you can use the paper soon after preparation. So it would be a good method if you’re in a hurry.
But in my tests this method does not work !
Taping the paper with masking tape before soaking defeats the purpose completely. The paper expands when wet, then when blow dried it seems to go back to a flat surface. But when you paint on the paper even with a medium wet wash, the paper buckles anyway !
Feel free to give it a go, but frankly I wouldn't recommend this technique. This is not what I call paper stretching.
Pre stretched watercolor paper
I see a few artists claiming that watercolor blocks are pre-stretched.
Watercolor blocks are a stack of sheets that are bound together with thick adhesive around all four sides. Block papers are not stretched. However they do seem to resist warping better than loose sheets.
I find that watercolor blocks still buckle when painting with heavy washes, but the paper flattens when it dries. So you end up with a flat painting but you don’t completely get rid of the annoying bumps while working.
Blocks can however be very practical for plein air work.
What’s the alternative to stretching paper ?
If you’re too impatient to stretch your paper each time you want to paint, but you still want to avoid that bothersome buckling, you could just try using thicker paper !
Like a lot of watercolorists, I use Arches watercolor paper for a lot of my work.
But did you know they make thick watercolor paper with a weight of 300 lb / 640 gsm?
This type of paper is so heavy that it only buckles slightly after repeated wet washes. 640 gsm paper is thick enough to resist warping even for wet on wet techniques.
This is almost like cardboard ! And on top of that you can get this paper in block format. So you get some of the benefits of a watercolor block (which helps to hold the surface flat) and a lower amount of buckling because of the thickness of the paper !
Not a bad option !
Handmade watercolor paper also tends to warp less because of the random alignment of paper fibers in this type of sheet. Handmade air dried sheets tend to cockle less and in random way which is evenly distributed over the whole sheet. But if you can get very thick handmade paper this is an excellent surface which needs no stretching.
How to flatten a watercolor painting
So you didn’t stretch your paper and now your painting is all wonky ?
Not to worry. There are ways that you can try to recover a painting which has buckled after a painting session.
The simplest method for flattening wonly watercolors is as follows:
1. Dampen the back of the watercolor painting using a water spray bottle.
2. Sandwich the painting between two sheets of clean paper.
3. Place the painting on a flat surface and cover with a board of some sort.
4. Now place weights on top of the board (some heavy books will do the job). The board will help distribute the weight across the paper surface but try to spread the weights out evenly.
5. Leave for at least 6 hours to dry.
Some people use an iron to flatten buckled paintings. Be very careful if you try this method because there’s a real risk that you’ll burn the paper, so use a low heat setting. Moisten the back of the paper first then iron the back of the painting, with a towel placed on top for protection.
If you can’t stand buckling, try preparing your sheets of watercolor paper in advance. Personally, I like the board stretching method using a plexiglass sheet so I can transfer my drawings, or the lightweight advantage of using stretcher frames.
Stretch paper only when necessary and when it suits your painting preferences.
If you reached the end of this long article, congratulations !
Now go have a good stretch !