Hi, Sometime ago I had succeeded in creating a texture from an image of a wooden object (the Wood textures in Sketchup, even Pro are very poor), but I don’t remember how I did it.
I thought it had perhaps been kept automatically in the materials, and that I had only to pick it up there, but it isn’t.
In my design I have some objects with that texture, but I may not apply it to other ones.
Isn’t there somewhere a bigger collection of textures that one may import?
No. You have to save the material(s) out to a collection. What version of SketchUp are you actually using? Your profile says you are using 2017 Make but you posted and mentioned SketchUp Pro.
You can either save your materials as a local collection via the Details menu.
Or if you have a collection already set up, you can open the secondary pane of the Materials panel and drag the thumbnail from In Model to the collection.