I'd recommend throwing the pieces away.
What is the BEST WAY to CLEAN chess pieces?
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I laud your approach. Of course, if these are wood pieces the bleach soak has already destroyed them, and if plastic the autoclave will certainly melt them. Either way, your problem is solved. Time to buy new chess equipment.
LOL!
There are some fabulous trolls on this site.
I usually place mine, every 6 months, all lined up on the roadside kerb, and the street sweeper comes along and waters them. Of course you do lose a number of pieces over time - some get stolen or disappear down the drain - but they're cleaned really well. I still have 7 left.
car wash.
Power wash those pieces with a mixture of bleach. Then send those rugrats parents a bill for the cleaning, stress, and punitive damages.
I usually just put the contaminated pieces in a bucket w/ Garra rufa fish and wait for them to nibble off all the dirt. Kind of a chess pedicure...
Oh, this is no problem.
I make sure that when the dirty little rugrats are around I use one of the early production CB Dubrovnik Red stained sets.
Everything on the little tykes just turns red and does not stick to the pieces.
I wiped my set down one time, a wooden set, I wiped the 'wood wax coat' right off my king, almost like I used extremely light sandpaper.
As far as your pieces OP, I would suggest talking to the Iranian government, maybe you could get them blasted by a practice nuke missle(of course it would all have to be top secret).
I have a set made out of Glass, so I use the dishwasher.
lol
Soap.
Suck on em for an hour.
Next time you have to take a massive dump, bring your chess stuff with you.
You might want to reconsider who you make friends with. Either that tattoo maker is a complete idiot or he's your mortal enemy and wants to ruin your equipment.
Nuke them from orbit... it's the only way to be sure. 
Youre supposed to clean em?
Yesterday while at my local chess club some children got a hold of my board and pieces while I was in the lavatory dealing with my chronic IBS. I caught them red handed playing on my equipment when I came out of the lavatory! By the looks of them they were snot nosed, unkempt, and very greasy (unreasonably so). I took swift action and swept the contaminated pieces into a plastic shopping bag and tied it shut to contain all the contagions my equipment had been infected with by these two miscreants. Once home I put them in a 50/50 bleach and water solution and let them soak over night. My good friend Vsevolod runs a tattoo parlor and said he would allow me to disinfect my equipment in his autoclave and I will bring them to him for this tomorrow morning. I think three hours in the autoclave should be adequate but would like your considered opinions.