Ah. Another trick is to paint the surface of the pitch with melted beeswax before pressing with a string mesh, and the next polishing session, something I did long ago when making some mirrors.
You might find some of the posts in this thread interesting
https://www.cloudynights.com/topic/7...-vs-polishing/
In particular with soft pitch I'd be worried at the possibility of turned-down edge, but one of the posts indicates polishing underwater (ie the mirror and the tool are both submerged in a waterbath) is beneficial in preventing TDE. Aside from the quality of the polish.