min, I hope you like that I show here your collage, so all the friends can see it without looking for.

 

 

 

About mount's colour I have the exact contrary idea than your teacher. Grey is the most neutral color and that is the job of a mount, to don't interfere with the painting.

 

Double sided tape? I have never done collage but that seems to me as temporary, to let move objects if you want. To finish  I suppose that paste is better. Tape also makes spots by the time.

 

I like the way you put the bottles. Let us see it when ended.

 

Ciao