Lapping heatsink - Which surface?

[Noto]

Hi all,

I have read a few guides that advise the use of a piece of glass or mirror. I cannot get hold of those atm but what i do have is a laptop screen from a broken laptop (the screen has a hairline fracture on one corner) Would this be just as flat as a piece of glass or mirror?

thx in advance

noto

 

[Noto]

how about the base of a pasta bake dish? ^^

also a quick question, do i want to soak the wet n dry paper or just poor some of the solution on top?