Permanent numbering options include using an engraver to mark stainless (https://www.grainger...g!439044756658!) the pro here being that anyone can use one, it's fast, easy and permanent. Cons are that it's still hard to see compared to a sign, and you risk creating deep uncleanable gouges that could harbor biofilms. Depending on where they are they may or may not be a big deal, but it's a potential microbial concern.
The other common option is to use filler material from a mig or tig welder (preferably tig for a smoother finished weld). Takes someone who can use the equipment, but permanent, easy to read, and smooth good welds will not have the harborage concerns above. (example, imagine without being painted over: https://www.google.c...iact=mrc&uact=8)
QA Manager and food safety blogger in Oregon, USA.
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