Cleaning Very Old Pots

[Lumaca]

I was doing some work in my mom's yard and found these 2 ceramic pots literally half buried in the ground in surprisingly good condition. No cracks but severely discolored and with a lot of residue (I'm guessing calcium?) I tried cleaning them with soap to no success, but maybe anyone here has any suggestion? Maybe some household chemicals that can restore these to their original color (or maybe make them look presentable)?

 

[meushi]

I recently cleaned up old pots that were covered in limescale. It was as simple as giving them an overnight citric acid bath... 2 or 3 tablespoons of citric acid powder in a sink full of hot water, place the pot in the water and give it a good wipe the next day.

 

[penumbra]

I recently cleaned up old pots that were covered in limescale. It was as simple as giving them an overnight citric acid bath... 2 or 3 tablespoons of citric acid powder in a sink full of hot water, place the pot in the water and give it a good wipe the next day.

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That is the right idea but I use a vinegar soak and a stiff toothbrush. Then soak it again to remove vinegar. I normally would soak it twice in the rinse water changing it after 24 hours.

 

[sorce]

Wheew!

You're not supposed to clean antiques!

I'd test a spot on the bottom.

Sorce

 

[Leo in N E Illinois]

The change in color of the clay and glazes is natural, and no attempt should be made to remove this discoloration. Patina is the name for this change in color.

Lime scale, does need to be removed if possible. Scrubbing pads, steel wool should not be used, as they will scratch the clay finish. Only soft brushes, or soft cloths should be used.

Weak acid baths really help. Key is weak. Strong "plumbers drain cleaners" are far too aggressive.

One technique, for scale that does not come off with a wash in vinegar or citric acid, is to bury the pot in peat. Use a large nursery pot filled with peat. Bury the pot completely. Set the pot where rain will wet and flush through the pot. Key is that it is rain water, with near zero dissolved calcium. This won't work as well in dry areas where you would need to use irrigation water. It may take as much as a year, but slowly, gently the organic acids in the peat will digest away the calcium. For light colored clays the humic acids may stain the clay a slightly darker color, but this color is in the same range as natural patina, and generally is not considered a problem.

Key is to not scratch the glaze or the clay in efforts to clean high quality pots. Also key is to not remove the patina. "Looking like New" is actually contrary to the artistic aesthetic of bonsai. Clean, but old, old as the tree the pot contains is the look that one should strive for.

 

[meushi]

I'll try the peat and rain water for a Tōyō drum pot on which the buildup survived repeated citric acid baths. I suspect the buildup isn't simply from lime scale and may include lime sulfur stains.

 

[Lumaca]

The change in color of the clay and glazes is natural, and no attempt should be made to remove this discoloration. Patina is the name for this change in color.

Lime scale, does need to be removed if possible. Scrubbing pads, steel wool should not be used, as they will scratch the clay finish. Only soft brushes, or soft cloths should be used.

Weak acid baths really help. Key is weak. Strong "plumbers drain cleaners" are far too aggressive.

One technique, for scale that does not come off with a wash in vinegar or citric acid, is to bury the pot in peat. Use a large nursery pot filled with peat. Bury the pot completely. Set the pot where rain will wet and flush through the pot. Key is that it is rain water, with near zero dissolved calcium. This won't work as well in dry areas where you would need to use irrigation water. It may take as much as a year, but slowly, gently the organic acids in the peat will digest away the calcium. For light colored clays the humic acids may stain the clay a slightly darker color, but this color is in the same range as natural patina, and generally is not considered a problem.

Key is to not scratch the glaze or the clay in efforts to clean high quality pots. Also key is to not remove the patina. "Looking like New" is actually contrary to the artistic aesthetic of bonsai. Clean, but old, old as the tree the pot contains is the look that one should strive for.

So you're saying they should go back to the ground again! I think I'd try @penumbra 's vinegar toothbrush method first, since I've got them laying around the house. They're not gonna win any beauty contests anyway so I don't mind the discoloration. Was just interesting that I was running out of pots yesterday and suddenly two popped out the ground (literally).

Interestingly, the inside of the pots are a good deal cleaner. Probably thanks to the glaze and the fact that they are upside down in the ground.

 

[jaco94]

I have often read that the patina of time is the most beautiful color of pots, it brings life to the trees, in my opinion you shouldn't try to refurbish them.

This contributes to wabi sabi, a notion of Japanese aestheticism particularly suited to the world of bonsai.

Beauty comes from the passing of time, from the sobriety and simplicity of the materials if possible, simple, natural, from imperfection ...

 

[RKatzin]

As a tile contractor I used a lot of muratic acid for both a final wipe down on new installations and to rejuvenate old ceramic tiles. Also great for new unglazed pots to remove production smudges. You can get it where tile and supplies are sold or at pool and pond supply places where it's used as a pH balancer.

 

[penumbra]

All of these suggestions are good and will work, but what do you have around the house? Vinegar and an old toothbrush I warrant. I can also add that I have done this to remove lime scale from dozens of pots, many of them bonsai.