The Little Brass Box Company and struggled to find suitable brushes for it. The problem is, of course, that when in transit, the brushes slide up and down in their tray and the hairs become misshapen which results in damage to expensive brushes.
Originally, I'd had a set of W&N Series-7 brushes in the tray and could now kick myself because a couple of them were spoiled. Once I realised what was going on, I started to insert a sponge which trapped the brushes in place when the lids were closed but even that only prevented movement if the box was transported carefully.
The eventual answer came when I spotted some Travel Brushes from Ken Bromleys in Bolton. They were made by a company called Escoda who are endorsed by none other than John Yardley and they're made from Kolinsky Sable. They come in light metal tubes and can quite literally be thrown about inside a paintbox or bag without any fear of damage. Most travel brushes are limited by the fact that you need them to dry out very thoroughly before putting them away, but luckily, the Escodas have a ventilation hole in the end so that you can close them up without worrying too much. Obviously, you would need to remove as much moisture as possible before storing, but there isn't the same worry of mildew forming as there is with other designs. Irrespective of the ventilation, it's always a good idea to dry them when you get home.
In use, the protective cover tubes form part of the brush handle and you end up with a very comfortable length and don't feel like you're having to compromise. The brushes hold a good amount of water and quickly come to a point. The range includes sizes 2,4,6,8,10 and 12, although they seem a little smaller than other brushes of the same marked size. A full set at Ken Bromley's costs less than £70. Now that's a bargain!!
I like them so much that I often find myself reaching for them in the studio as well as outdoors.
I also have a set of Winsor & Newton Series-7 Retractable brushes in a small Field Box. I bought them years ago and although they're very neat, they're not the slightest bit comfortable to use. In fact, when using them, there's a tendency for the brush to start retracting! They're very annoying but I can't throw them away (or even bring myself to sell them), LOL.