How to flatten a watercolor painting is a process anyone should know before painting a beautiful piece in watercolor. I have two methods on how to flatten a watercolor painting. One approach is for mild cases of buckling, and the other is for severe cases. Both ways employ the use of moisture and pressure.
The moisture in watercolor on just one side of the paper causes that side to expand. The opposite side remains dry and unchanged; the expansion on only one side of the paper causes buckling. Although there are methods to prevent buckling from happening in the first place, the techniques I’ll share focus on watercolor paintings that have already dried.
Method 1: Moisture and Weights for Mild Cases
The first method I have is quite simple and poses minimal risk to your watercolor painting. However, this method will not always work, depending on the severity of the buckling of the picture. I suggest you try this method first, though, as the second method might ruin your painting.
- The materials required for the first method are as follows:
- Spray bottle
- Sketch or copy paper (should be longer and broader than the painting)
- Towel (optional)
- Flat board
- Flat weights (books often get the job done right)
Step 1: Misting the Underside of the Painting
Use the spray bottle to mist the underside of the painting – the side opposite the drawing. It is paramount that you use a spray bottle with a fine mist spray. A fine mist spreads the moisture the most evenly across the surface of the paper. If the paper’s surface does not receive even amounts of moisture, the different drying times will cause buckling.
Step 2: Cover the Painting with a Sketch or Copy Paper
Place the sketch or copy paper on a clean, flat surface. Then place the painting image-down on top of the sketch paper. Make sure that the sketch or copy paper is larger than the painting to cover the entire drawing.
Step 3: Cover the Other Side of the Painting
You can use another sketch/copy paper or a clean towel to cover the other side of the painting. The painting should now be sandwiched between two pieces of sketch paper or a sketch paper and a clean towel.
I prefer using a clean towel to cover the side of the paper opposite the drawing. A clean towel helps the moisture dry evenly across the surface of the paper.
Step 4: Place the Flat Board on Top of the Sketch/Copy Paper or Towel
The flat board, anything flat that covers the entire painting dimensions, is the primary tool for flattening the watercolor painting. At this point, the pile of materials you have from bottom to top should be as follows: sketch/copy paper, image-down painting, sketch/copy paper or clean towel, flat board.
Step 5: Put Weights on Top of the Flat Board
Here’s the last step in this process. Putting weights on top of the flat board will force the watercolor painting to adopt the board’s shape, which is flat. If you don’t have weights, you can use books to significant effect.
Each step in this process forces the watercolor painting to flatten. Misting the underside of the picture expands its surface just as the watercolor did the other side. The sketch/copy paper and towel combo ensure that the moisture dries evenly across the surface of the painting, preventing buckling. The flat board is the instrument of flattening the picture. And the weights are the force that makes the painting flat.
Check the painting every two hours to see if it isn’t buckling. Replace the sketch/copy paper or towel on top of the image if it gets too damped. Check the painting and replace the paper/towel on top until there’s no more wrinkling or the underside of the painting is no longer damp.
Once the painting is flat or no longer damp, place another dry paper or towel on top. Place back the flat board and the weights. Then wait for 24-72 hours to ensure the painting thoroughly dries flat.
Method 2: Moisture and Heat – the More Drastic Solution
This second method is more extreme and poses the risk of ruining your artwork. But if the first method does not work for you, this one’s worth a try. This method employs heat using an iron. So, if you’ve never done this kind of thing before, try it on a blank piece of paper first to see what temperature works best.
The materials required for this technique are as follows:
- Flat iron
- Spray bottle
- Sketch/copy paper
- Clean towel
- Flat board
Step 1: Do Steps 1 to 3 of the First Method
Do the first three steps of the moisture and weights method. Mist the underside of the watercolor painting, then put it image-down on a sketch/copy paper. Then place another sketch/copy paper or a clean towel on top. Again, I prefer using a clean towel to cover the damp, blank side of the painting.
A towel is safer for this method. It’s thicker, so it will absorb most of the heat of the iron. A piece of paper is thin and more flammable; it’s riskier to use.
Step 2: Use Iron to Gently Rub the Surface of the Sketch/Copy Paper or Towel
Set the iron on medium-low and gently rub it on the surface of the sketch/copy paper or towel on top of the painting. KEEP THE IRON MOVING across the surface; don’t let it rest, or it may burn the painting.
Heat the iron as needed to allow the moisture to relax the paper’s fibers. But make sure the iron is not too hot that it burns through the painting.
Step 3: Replace Damp Sketch/Copy Paper or Towel
Once the painting is mainly dry, replace the sketch/copy paper or towel on top of it with a new one.
Step 4: Do Steps 4 to 5 of the First Method
Place a flat board on top of the new sketch/copy paper or clean towel, then place weights on top of the board. Check the painting every 2 hours and replace the covering paper or towel if they get too damp. If the covering paper or towel no longer gets damp, return it and place back the board and weights for another 24 to 72 hours.
My methods on how to flatten a watercolor painting are relatively simple. But they require a lot of patience. Waiting for the painting to completely dry is perhaps the most challenging part of these methods. But if you want to achieve a flawlessly flat watercolor painting, all the waiting is well worth it. If you want to learn more about protecting and storing watercolor painting, you can find my guideline here.