Call me wrongheaded, but I've NEVER lapped a barber hone and never regretted it. The closest I've come to this is to rub two of them together to help get rid of some ground in steel.
IMHO (which could, of course, be wrong) barber hones are not designed to work with a slurry, none of mine have even remotely dished or any such like a water stone does (after all, water stones release their particles into the "slurry" which does the sharpening-barber hones do not).
I've lapped a spyderco hone, but not a barber hone.
So far, perhaps I'm just lucky, but they continue to do fine.
Often, rather than even scrubbing as in the above example, I'll just hit them with oven cleaner. Soon after, they are as good as new.
Let the flames begin...
John P.