I just had a Blue Diamond put in a vice and pressed for about 10 min. Tip cut great, the sides were burnished with super glue and the tip plays fantastic. My question is, mine was pressed for 10 min while others say they press them for hours and some for days. What's the point of pressing them that long. Mine was Not soaked in milk. Thanks.
Obviously the leather compresses under pressure but it also tends to relieve and expand slightly after the pressure is relieved.
In theory, longer held compression tends to expand less after the pressure is removed.
Some get quite scientific with measurements (thickness and/or durometer readings) before and after attempting to achieve a specific amount of final compression in hopes of having a repeatable process.
It can be fun and interesting experimenting with tip compression methods.
If you really want to experiment, try one of my old "Double Compressed" methods:
Press a BB into the center of a Triangle tip (Triangle because they are thicker).
Press the entire tip surface slightly beyond the BB thickness.
This obviously creates a considerable dent in the center of the tip that is later removed with tip shaping.
The concept is to create a super hard center with less hardness (for spin) once you get outside of the center.
Must have put 20 to 30 of these on long ago; I still have a few of these in my box as I still get the occasional local request for one.