Cwdjrx _ wrote:

In the US, there is a commercial product called CLR that often will
remove many calcum-lime-rust types of stains(hence the name). It can
clean up coffee pots that can become very stained. It is widely
available in some home improvement stores and supermarkets. Be sure to
read the instructions carefully. It contains glycolic,sulfamic, and
citric acids as well as surfactants. If it works, it works fairly fast
and long contact is not suggested for most surfaces. I have used it on
coffee pots and a rust stain on a bath tub, but not on a decanter yet.
This might be a good last resort if milder cleaning methods fail and you
can not justify the expense of professional polishing.

IIRC, you've quite knowledgable about chemistry, so forgive me if I state
the obvious: the CLR is designed to remove inorganic salts through
chelation and probably won't do much on the presumably organic residue left
in a decanter. The surfactants might possibly help loosen the deposits,
but then so too would alcohol or soap.

Mark Lipton