And I thought this was 1/2 pint to 1 imperial gallon

As an aside my coffee cup develops more sludge than OH who drinks hers black so potentially complex issues with protein binders as well as saturation levels (she dilutes her coffee more) and residual water minerals still in solution.

for several years as a student and after I worked in various backstreet garages businesses that shared a common yard. As the junior I had to make the tea which stained the mugs with tannin and every so often bleach them out.

I remember a deep philosophical discussion – did the bleach remove the tannin or just bleach it so it was still there but invisible against the white inside of the mugs?

.

I’ve not noticed it, because neither of us takes sugar [and anyway, I drink black Coffee] … But it does seem reasonably logical.

The micro-surface of the cup will almost inevitably be pitted; forming sites where limescale [and tannin] deposits take-hold.

I would posit that the Sugar effectively ‘gets there first’ and forms a protective layer [similar in concept to Teflon coating?]

MichaelG.

Tannin stains in tea cups remove very well with a washing soda solution. Sodium hydroxide works as well, but will etch the glaze on the Cups.

Since we drink tea by the gallon in this household we often have a couple of mugs soaking by the sink.

And if you use CIF it will adequately clean the tea stain, but produce fine scratches on the cup and spoon that then increase the rate of brown stain depositied. Contains limstone dust as a 'mild' abrasive.

Bill