So, I found a small picture frame for next to nothing. This is the result:
The formicarium is about right for a first founding chamber, I think. One lesson is that I found out that cooking oil is a much better mould release than soap water. This formicarium won’t open up for cleaning but the entrance is quite large and I think I’ll be able to clean it when I have to.
Since this is an old frame the glass is slightly domed. I wonder if this will help viewing the tiny ants.