Is it safe to clean the tarnish off items like silver bars and rounds with the boiling water, aluminum foil and baking soda method?
Why? Sell them for 20 times their value on Ebay as "high end toned pm". Seriously, why? The toning is technically still silver, and its protecting the rest of the silver from tarnish. Just leave it be and change the storage conditions under which you store them to prevent any further toning if you can. Heck, I use fresh silver to keep the rest of my coins from toning.
I just bought 3 moderately toned/tarnished bars from a local shop today. Can a certain level of toning hurt the value of the bars (like if the whole bar were to become brown-black?)
Does it still weight the proper amount? That is the major issue. If it becomes corroded to such an extent it starts losing weight it might, but that would be the "matte black" stage of corrosion before that would occur. If it truly is "matte black", then I would agree its best to clean it to stop the corrosion. Short of that, simply leave it alone. If you truly despise the bars, go to a coin show and ask to trade them for something you like, (with an associated fee of course).
I don't mind the fact that they are a bit tarnished. I was just worried (after I bought them earlier today) that it might make it difficult for me sell them in the future.
You could just get a 'silverware cloth' that has chemicals in it and wipe and polish. Some have chemicals that limit further oxidation. I do not consider bullion or rounds as numismatic items although some do, and so just use a silver dip if they get ugly. Apologies to the former collector types. Welcome to the forum. Jim
While there are some exceptions, most bars and rounds don't carry a premium over melt. They are probably fine just the way they are, but if it bothers you, give them a dip. They should come out shiny and the value will still be the same.
Some people treat the silver bars/rounds just like numismatic coins, others don't. It's your bar/round, your choice. I would say, however, if you do want to clean them, then dip them in the E-Zest(I think that's the name of it) like some do with coins. I would suggest researching the bars/rounds first before you do clean them.
After (If) you clean them, I'd suggest putting them in ait-tites. They have cases specifically for bars and rounds.
What about a 10 troy oz englehard silver bar, with eaffling on the back, that I want to sell? Light brown over the silver? Should I clean it a bit before selling on ebay?
Depending on the look you may be costing yourself money. MS-70 works reasonably well on most things though