Karl, thank you very much for your help.
I´m not sure, how to add some "earth-material", but I have some material (from my previous project, a german WW2 gun in snow), from which I would use some material.
"Real mud" would be a good solution, but I have some "problems" with the "organism", which live in it.
My actual status on my diorama:
Due to my trembling hands, I made only a few additions.
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I used 3 colors to paint the wooden walls.
Revell glossy black and "ochre brown" with some real pigments of a black.
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The image shows the difference between the painted and a "fresh" wooden part.
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Hmm, the wooden construction seems to be to small - using my image as a reference.
Perhaps I can use some "earth" for fixing this. (I would use a wooden material for adding in height)
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Also the table had to be repaired - this time with real wood-glue.
(2 table-legs were glued)
greetings...
Soeren