How to remove stains from Chinese tea set

July 6, 2019 7:31 AM

I received a Chinese tea set from Singapore. It was well thought of, though had been in storage for many years. The rest of the tea set is in good condition, however the container that is meant for the storage of the tea leaves has these unusual white marks on the outside. Any idea how these marks came about, or how they could be cleaned?

Photo 1
Photo 2
Photo 3

I tried cleaning a specific spot with a toothbrush, but it doesn't seem to have made any difference. The pattern of the marks is almost like a salt had crystallized on the surface. The appear only on the outside, the inside appears clear as with the rest of the set.

posted by Gomez_in_the_South to Grab Bag (6 answers total)

It's an artifact of the heating or glazing process and can't be removed -- trying to do so will just cause damage!
posted by DarlingBri at 8:00 AM on July 6, 2019

Response by poster: Thanks DarlingBri.

Would these artifacts have been like this from new, or is it likely that they have spread/grown over time?
Is there any other name for this - I'd be interested to see other examples.
posted by Gomez_in_the_South at 8:11 AM on July 6, 2019

Best answer: Are you saying that these spots are new? I can't tell for sure from the photos but it looks like the pots may have been fired with some kind of low fire technique, and they don't look glazed to me. I think the dark brown is the clay colour. If they were low fired then the clay is porous and you may have some kind of crystalline growth or staining on them. Sort of like you might get on a terra cotta flower pot. Depending on how precious they are I would try putting it in the oven on a high temperature, warming up and then cooling down slowly, to see if that gets rid of it. The only issue with this is that if there are existing cracks or weaknesses in the pot high temperatures can exacerbate it. If the pot is structurally sound then it should hold up fine to high temperatures in an oven. I refire low fired stuff all the time in a ceramics studio as part of the decorating process.
posted by Cuke at 8:28 AM on July 6, 2019

Maybe I should add that "low fire" in ceramics terms means about 1700F - 2000F so your oven won't get that far but it may still work.
posted by Cuke at 8:32 AM on July 6, 2019

Response by poster: I don't know how they appeared in the past, but imagine that it wouldn't have been bought in the condition that is currently appears.

There is an oven used for firing ceramics at a maker space nearby, so I could take it there to try that, cuke.

Whilst the set has sentimental value, the difference for this particular piece is quite jarring as is, and it could be substituted with another container if necessary, so we'll likely take the risk.
(will stop threadsitting now)
posted by Gomez_in_the_South at 8:52 AM on July 6, 2019 [1 favorite]

Best answer: It's likely efflorescence, a phenomenon often seen in bricks. Naturally occurring salts bloom out of the inner areas of a clay object to settle on the surface. It's far more common in humid places or where there's exposure to water. Mechanical removal is least damaging. Maybe try a very fine steel wool. People also use muriatic acid, but that could permanently damage other minerals in the clay.
posted by quince at 9:38 AM on July 6, 2019 [4 favorites]