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I bought an old Imari bowl at an estate sale this weekend which had apparently been used as a planter. No hole had been drilled in the bowl, but a heavy calcium/lyme type of deposit was left around the upper inside of the rim. What is the best way to safely clean this?

I'd also like an opinion of age, if possible.

Thank you.

Hi Patti & Ernest,

Vinegar and other household calcium removers will not harm 'hard paste' (highly vitrified porcelain) because when properly fired the body and decorative enamels essentially transform into a form of glass inside the kiln. If the piece is 'soft paste' (incompletely vitrified pottery) the acid in these liquids will eat away the unbonded calcium, creating quite a mess. Chlorine-based bleaches will do the same damage to soft-paste dishes, though hydrogen peroxide bleach is safe for them.

Determining whether you have true porcelain or pottery can be a chore. A rule of thumb is that crackle-finish ware probably is pottery. Also, pottery doesn't usually ring like porcelain. Further, highly vitrified porcelain and its glaze can't be scratched with a steel blade, but be careful and find an inconspicuous spot on the bottom if you wish to test the piece in this manner.

I cautiously mention that some but not all types of fine wood-sanding pads use an abrasive that will not scratch glass or hard-paste porcelain, but they will remove gilt decoration, so use them only as a last resort. These pads typically have only one side of the foam rubber square impregnated with abrasive. I use a brand called Norton 3X #320 Ultra Fine Grit. Again they should be used only with hard-paste porcelain and only on vitrified surfaces, never on gilt-decorated areas. I use them only to get rid of some of the more resistant patches of calcium after applying vinegar or another household calcium removal solution.

Best regards,

Bill H.

We used a light vinegar solution for soaking. I am not an expert in this field, and so you better wait for other advise.
Ernest

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