they can be both
I love stamps, and I love postcards, so postcards of stamps are really a match made in heaven. I only ever use boring click-and-drop mailing printouts so never get to actually use stamps. I saw a Royal Mail post on Instagram about the duck themed stamps and saw on their shop that they do postcards of said stamps, and then discovered that there are a whole load of designs available. I bought the ducks, the river wildlife, and the Peanuts ones because, why not. I have an IKEA pegboard above my worktable and I use postcards to mix up the decoration by clipping them to the various containers and baskets I have hanging on the pegboard, so it’s nice to vary them. I also thought the river and duck ones would be good reference images; I do enjoy using a non-screen reference when I can.
I would really like to expand my illustration practice to include just general illustration work but that feels quite scary and exposing, as normally I can rely on the very narrow brief I have with the logbooks, and the idea of trying to market just illustrations requires a different mindset. I do really love painting wildlife though and feel I am getting to grips with things other than birds so I might try doing something a little more formal in that regard. With this in mind, I painted a Dipper and a brown trout from the postcards:

I might add some lettering, like I did with these fish. What do you think?
