Material — brass, leather, oak, steel — is recorded on every product as a filterable attribute rather than as a collection of its own. Finish is recorded the same way. If you are shopping by material, start in the collection that matches the job and filter from there.
Made to Order works differently from the other four. Those pieces have variable scope and no fixed price, so they carry an inquiry instead of an add-to-cart button. Nothing is quoted until we have understood what is actually being asked for.