I have written about partially filling palettes so you leave some space for mixing in the pan or palette, but I am often asked about how to fill pans or half pans or palette wells with watercolour. It isn't difficult to do but there are a couple of tips that will help you to get the best results.
Before you start filling pans, half pans or palettes, you will have decided which colours you are using so I won't go into that here. I'll talk about half pans/pans in this post as that is the system many use.
First of all, shake the tube well. Some colours separate in the tube and the tubes may have been stored for a while. Hold your fingers of one hand at the bottom of the tube, on the widest part, ready to gently squeeze as you take the lid off just in case the paint comes out suddenly - you can gently give the tube a squeeze and effectively suck it back in again.
Squeeze a little paint into your pan. If you notice some gum arabic coming out, shake again. Once you are ready, squeeze the watercolour into the corners of the pan and half-fill. Stir the paint with a toothpick or a blunt needle (something fine will not waste the paint) and allow to dry. Once dry, fill the rest of the pan, not completely to the top but close to and stir again. Allow to dry, in a well aired place - like a windowsill. Don't close the palette. I tend to allow to dry leaving the pans at an angle (see my other post here) but that is up to you. Depending on how dry the environment is, it make take a couple of days or a week to prepare pans of watercolour.
Most companies use the same formula for their watercolour whether they are making pans or tubes, though some only make tubes and some only make pans. Winsor and Newton make both but they use a different formula for each. If you wish to refill a W&N pan or half pan, I find the best way is to add just one drop of glycerine to each half pan of watercolour. I find Art Spectrum watercolours need a little more than 1 drop per half pan. If you are using Cotman student colours you will definitely need to add some glycerine or then will crack and fall out of the pan. Da Vinci don't need any additives - they are incredibly creamy and consistent and dry beautifully. Daniel Smith mostly dry beautifully, though some to the primatek colours could do with a little glycerine. Some of the colours are more liquid from the tube so be careful when squeezing them. If they are more liquid they are more likely to crack as they dry so perhaps pour just a third of a pan at a time.
Some watercolours will crack a bit but not so much that they fall out. Next time you fill them, add a touch of glycerine to overcome this.
Some manufacturers use honey to keep the paints moist - such as M.Graham and Sennelier. I find the M.Graham paints too wet for Australia though as they never fully set. They may be fine in a drier climate. I have never chosen to add a drop of honey to my pans though I suppose you could - I'd be afraid of attracting insects!
Once the pans/half pans are dry you can put them in your palette and get out and paint. I don't tend to spray my watercolours before use, though I know many artists do. I find the Daniel Smith watercolours I use simply don't need it but if you want a more luscious paint you can spray them or add just a drop of clean water to each colour before use. If you play to do that, gently press your finger into each pan before it has fully hardened to make a little dent that will hold the water.
If you are filling palettes directly, you can do it all at once but make sure you squeeze the paint into the corners, not just a squirt in the middle.
I will add photos but also have a look at this excellent post by Brenda Swenson that shows a great travel palette nicely filled with watercolour.