This is a stackable shelf module sized to fit standard 25mm diameter dropper bottle such as those used by Vallejo or AK Interactive.

It is not a complete one-step shelving solution. The modules will need to be glued together, and the whole set will need to be secured to a base-plate of some kind to keep it from tipping over. Depending on the number of layers, some support for the rearmost shelves may also be necessary.

There are separate STLs for the bottom, top and intervening shelves. The bottom and top pieces are not strictly necessary, but they make a more compact unit.

I've also included STLs for bracing pillars for the back shelves, 1, 2, and 3 level tall. If a higher pillar is required, two of the shorter ones can be glued together.

Edit 2023-05-05: I've now added a pair of stepped brackets which tip the whole shelf assembly forward by about 20 degrees, which reduces the depth of the shelves and makes them more compact. The bottles are still held securely by their collars and the lipped shelf beneath.

Edit 2023-05-07: Added STLs for a narrower 130mm shelf set — they only take four bottles per shelf, but might be handy if you have limited space or only have a few paints to store. Plus they print a bit faster.