Altar clothes are not supposed to be starched - if they are, then one of their important functions has been defeated: absorption of the Precious Blood if accidentally spilled.
The Precious Blood is never spilled; in any event, that is the service of the corporal.
A mangle! Wow! BTW, Purificators are not to be starched; corporals, lavabo towel, and altar cloths are.
A mangle doesn't starch! It just pulls out the wrinkles! There is no need to starch a 100% linen altar cloth. Actually, no need to starch any altar linens if they are pressed correctly. This is a neat little mangle! They were also dangerous!
I recall seeing these in the laundry room of the NAC in Rome. Maybe used even also for bed sheets?
First the altar cloth is soaked in a long starch-water tray, then laid out flat to dry on a long laundry table.