That's madness. I did that in the far past: with soap. And it leaves the typical "washed coin" look for you to "admire". Not good.
The term "junk" is relative, buf if it is really that poor quality and you can give up un the numismatic value, then you can clean it with rougher detergents as well (I also tried this variant).
What is this 'numismatic' you speak of? Dealers have never heard of it when you sell silver. They only seem to acknowledge 'premium' and 'numismatic value' when selling to you. Hmmm ...I say it all the time: it all reverts to spot. The better looking coins will sell quicker or might grab a tiny premium from private buyers (usually negated by ebay or whatever fees or the time it takes you to search for buyers, though). Even ugly or basic bullion or junk silver will sell around spot if the market demand gets hot enough, so that is usually the smart thing to buy. The "nice" stuff just sells quicker, that's all. I just don't understand the numismatic crowd, esp for silver, which tarnishes naturally... expectedly. It's basically just a bunch of mustache twisters holding plastic-graded slabs and thinking their coins are worth much more than they would actually get if they traded them in today. It is like the guy who puts $30k in parts into a $20k car and then thinks it's actually worth $50k+ when he sells it. Curious.