I create watercolour palettes using all sorts of found objects and have shown a lot of them on my website here (https://www.janeblundellart.com/palet...)
I found a video I'd made a while ago of one of them that may show a little more information. I'll create others if they are helpful :-)
This was a cigarette case from the early 1900s - I don't know the exact date - that works well to hold 19 (or 20) colours using 19 Daniel Smith watercolour sticks. The colours are on my blog here: https://janeblundellart.blogspot.com/...

There are a couple of other posts about Watercolour Sticks on my blog - just search or use this link:
https://janeblundellart.blogspot.com/...
or this link:
https://janeblundellart.blogspot.com/...