Some of you may know this but I'll pass it along for the ones that don't.
After sizing cores. The lube has to be removed. I use a container and fill it with hot tap water, add a squirt of Dawn dish soap and then add Citric Acid. Shake it for few minutes and the cores will turn bright.
The lube will be off and the cores are also etched.
No more heating them up in a crock pot or on the stove.