So you've just bought a new watercolour box set and found out that some of the pans are falling out of the slots. There's actually a few easy ways to secure those pans and stop them from falling out.
This problem also happened to me in the past. And it's a problem that's quite common with Winsor & Newton plastic box sets.
The pans that come with Winsor & Newton (left) are smaller than those empty pans you can buy online. They fit nicely but not tightly in those box sets. Some boxes that have this problem are the Sketchers' Pocket Box and the Brush Pen Set.
Those small WN pans can fall out easily when you have the box upside down.
One way to secure the pans is to get Blu-tack, or White Tack (whatever colours they come in), tear off a tiny bit and stick it on the back of the pan.
Just squeeze the sticky tack into a tiny ball, and put it on the back. Next, press down the pan into the slot. This will secure the pan.
The second way is to put a drop of gum arabic in the slot, and put the pan back. This is good if you already have a bottle of gum arabic around.
Third way is not to do anything and just use your watercolour pans. When water and paint get into the gaps between the pan and the slot, the pan will stick to the box.
Sometimes when too much paint get into the gap, it may even be difficult to get the pan out. That's when you need to use a pen knife to loosen the pan.
How about securing the pans to those metal watercolour boxes?
Before you put your pans in, bend the metal tabs slightly first.
Next, slot in the bottom of the pan into the metal plate holder first, before pushing it in.
Do not slot the top of the pan in, it's not going to go in that way.
With some of these metal boxes, you may be able to fit another row of pans in the middle. To secure these, just use the sticky tab again.