I use a very watered down woodworking pva glue on 200x200 mirror tiles on one of my printers and the same mix on a 200x300 ali bed on my other regular printer. Spread the mix over the plate and let it dry. The adhesion is better on the mirror but is still ok on the ali. (I’m no chemist but PVA and PLA sound like they are nearly the same so my reasoning was they would likely stick together well 
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I started out using borosilicate glass but I found that used to splinter some times leaving pits in the glass. I only use pla @ 210 max with a bed temp of 60 max. Eventually the mirror cracks, usually when trying to spatula the print off the bed before letting it cool enough, if you leave it to cool properly the print usually lets go by itself with a satisfying ‘pop’.