They're art trades where you sketch a bunch of things for each other! They're a lot of fun and you get to draw a bunch of characters in little doodles instead of just one or two in something painstakingly detailed!
The entire cast of The Historians can be found here: [link]
And the entire cast of Londinium can be found here: [link]
(More information here: [link]
But if you absolutely want to melt me, you can do this with the cast of Comedian Heaven: [link]
(I spend a lot of time crying over double acts, especially Peter Cook and Dudley Moore and Laurel and Hardy. This is my life.)
Anyhow, send over some references of your characters if you're interested and I'll get to work as soon as possible!