I make them. Usually coat mine in epoxy so I know they are safe. I've heard using drylok paint is safe without epoxy, but I haven't tried it yet.
One in my 180. Obviously there is real wood also.
I've made 10 so far and have tried a couple different ways but all with epoxy. The one above was carved then coated in black epoxy and then painted with a paint that was supposed to adhear to plastics and epoxy. After about 2 years the paint was flaking off.
This was a sand waterfall. Coated in clear epoxy painted with acrylic paints. This thing was so strong it took me forever to destroy it. I used alot of epoxy to make sure the moving sand didn't damage it. Overall wasn't happy with design and it was made for my ex so when she became my ex it was destroyed. Lol
This is one of my first ones. Coated in cement and painted then coated in clear epoxy. Has been in use for over 5 years. Still set up today.
All attached with silicone to glass. Make sure when you attach it to the glass you make a bead around the perimeter to keep junk out from behind the background. Steps you learn as you go.