Recently, Tom0779 asked in a comment, on his painting 'Light at the summit' what exactly contact paper was. Jin7 and I replied to that and I like to share my comment in this article.
Contact paper is some sort of adhesive (Selbstklebend) paper. I use the kind that you can buy in a job-shop/hobby-shop on a roll, mostly that wil be 50cm wide and a few meters long. It is normally used as kind of protection paper in cabinets, drawers, etc.... It sticks on one side, the other side is somewhat plastified.
Also available on Amazon:
You can cut (cutter, scissors) any shapes in it that you desire and stick it on the canvas. PRESS hard and make sure the canvas is clean!! IF it does not stick enough, use some paper glue to stick it on the canvas. Afterwards, you can scrape the glue off and paint it over with white gesso if necessary.
Have a look at my painting 'A warm winter' to see the result of such action. Oh yes, some bleeding near the edges can appear, it is not abnormal. Again, there you can use white gesso, or even T-white to cover that up somewhat. The two pictures underneath will show the contact paper applied at the start and the finished creation.
As for different shapes, the sky is the limit! Various forms can be cut out of that paper or you can use mask tape if the desired form has no bending.
Here are some examples:
'Icy lake', before and after.
'Pastel seascape' before and after:
Good luck with that!