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Comment by perl4ever | Hacker News Reader

I was trying to find the best way to clean copper pots. Sometimes people note that ketchup works, but it's hardly cost effective. The most basic option seems to be salt and vinegar, but what could you add to it (from a minimalist perspective) to give it the clinging consistency and homogeneity of something like ketchup? I thought maybe cornstarch, but it did not suspend; it settled out.

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I don't have any copper pots, but vinegar is my go-to cleaner around the house. Try adding about 5 to 10 percent by volume to a fully flooded pot and let it soak for an hour or two, bring to a boil of you are impatient. This works wonders for my pots, shower, sink, etc.

Cornstarch water is shear thickening, wheras ketchup is, I assume, shear thinning.

Cornstarch mixed with water is shear thickening, but when boiled, it becomes shear thinning (AFAIK), and that is basically what ketchup is. If boiling it, you should use way less starch - it goes a long way. You can also use other other flours as well (not sure how different the performmance is), like you would in Béchamel or custards. I think the shear thinning effect comes from starch gelatinization [1].

I don't have time ATM to go through the whole paper, but it seems like [2] is covering exactly this topic in detail.

I think (but [2] might correct me, I'm just guessing at this point, please don't quote me) that there is no special connection between the mixture being shear thickening before, and shear thinning after boiling - just a coincidence in this case.

Source: sciency-cooking dabbler, don't trust what I say too much.

[1] https://en.wikipedia.org/wiki/Starch_gelatinization

[2] https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.85...

neat!

Bar Keepers Friend is great for most copper/metal cookware and other things around the house like sinks as well.

Put a lid on it, 1 cm of vinegar in it, then boil. Put it under an extractor hood or outside though.

You have to boil cornstarch to disperse it. Arrowroot can disperse at lower temperature but it's kind of obscure (around $3–5/lb but lasts a while). Powdered sugar might be a more practical option?

Yeah, I kept doing that for my copper pots once a month with different things: ketchup, bar keepers friend, etc. It was never an easy wipe away experience like I imagined.

The baseline for me is vinegar poured over salt, which magically removes tarnish in seconds without even wiping, in some spots. But in others, it doesn't and then it takes a fair amount of scrubbing.

So what I'm looking for is a way to make the reaction more uniform, perhaps slow it down. Maybe corn syrup.

Wet paper towels cling to the walls of a container and suck up vinegar from the bottom.

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