WHY?

How come tea stains (tannins, I think)deposit on the inside surfaces of my cups (ie mugs), but NOT on the inside of my tea pot?

They are from the same set. Made of same materials, as far as I can tell: same decoration, same glaze.

Also, I do not take milk or sugar, so the contents of both are identical.

Only difference I can ascertain is inside of tea pot is not exposed to light, so perhaps photochemistry at the base of this.

Ena, I am pretty sure that the inside of a teapot will be stained. You probably don't notice it because it is dark inside. Try slightly gently rubbing the interior with some very fine sandpaper and I am fairly sure you will fins a brown residue.

I was told to soak tea/coffee stained cups etc. with Steradent tablets, the ones used for dentures. It does work.

Similiar to Anne we soak teacups in Milton or tablets used for sterilising baby feeding bottles which ever is the cheapest

Soaking in Persil (other detergents also available) works, but there is always a nasty aftertaste!

There is a product called tannin remover. The difference between that and suggestions already said is - tannin remover gets rid of the tannin the other products just whiten it so it can't be seen.

My son lives near London and the hard water causes stains on cups and other problems,do not use sandpaper on any glazed pottery it will make it worse

Red wine, also apparently high in tannins, but I do not get any tannin deposits on wine glasses.

Wondering what it does then to human insides... As non-tea drinker of course

The simplest way to remove tannin stains is Bicarbonate of Soda. Use a sprinkle on a damp cloth or piece of kitchen towel, and rub the stains. Then rinse and wash...no taste and cheap. Two heaped teaspoons in a teapot topped up with boiling water and allowed to cool, rub around with a gentle sponge scourer and be prepared for all the gunge it will move. Again rinse and wash as normal. you can soak cups in the same way, but it is quicker just to rub with a damp cloth....... No scratching, funny taste or expensive.