I’ve read of several ways to clean the stains and hard water deposits from pots. They included scrubbing them with a scouring block, CLR, baking soda, soaking them in rain water, and even burying them for a few months.
This pot, a 40-year old Heian Kouso came to me with considerable calcium buildup, and while I wanted to preserve the patina it was developing, the buildup was distracting.
First up, CLR, a cleaning solution formulated to remove calcium, lime, and rust.
Nope.
Next, a Sand-flex block, used to clean tools. My concern with using this product was that the grit would etch the glaze, and/or buff away any signs of weathering.
I tested it on a couple small spots, and thought it was best to stop there for those reasons:
After some online searching, I decided to try a paste of baking soda and vinegar. It was allowed to remain on the pot for three days. At first it was hopeful:
But as it dried, the calcium deposits immediately reappeared.
So, on November 9, 2013, I buried the pot in my growing bed and gave it a few months to work.
4 months later in March ’14, I uncovered it to check on the progress:
It was showing some progress, so back in the ground it will go.
Liberated on 6/14/14 to check results after 7 months in the ground:
After cleaning it up and letting it dry:
Note the shiny spot on the left, from the sand-flex test:
It seems most of the calcium deposits are gone; though a few more months in the ground won’t hurt it any.
So a year to the day later, here is how it looks on 11/9/14:
Bonsai Pot Unearthed:
Rinsed:
Dried with a soft cloth:
Before/After:
It’s a bit hard to tell by the photos, but some pitting and inner-rim glaze chips that show up white are still white, but the calcium deposits that would show when in use were nearly gone after one year in the ground. I would not hesitate to use this pot for a local show at this point.
I think the results were better in the warmer months, but cannot conclude whether it was ground temperature or more frequent watering that contributed to those results.
Nebari Bonsai 
Wow…that is some hardore effort gone in there. I would forget where I had buried my pots, would need to make a treasure map. In japan we used to rub the pot with our nuts….(as in almonds, peanuts etc. ) softly abrasive and oily etc. Not sure how effective they werelong term but used to give me a sore arm from over rubbing.
(I am being serious)
You are a tortured monkey indeed 😉
Very interesting! Would never have thought of that.
Great Subject! I have a few that I haven’t been able to get clean, now I just have to give the pot up for a year to the dirt… What gave you the idea to bury it?
I’ve often heard people recommend burying a pot to remove the deposits, but nobody could ever produce results justifying the recommendation…so I thought I’d give it a go!
excellent!!
Have you tried using camellia oil? I have heard of that being used for tools and I think pots as well. I have also read about using walnuts. Walnuts go into a sock then you beat them around and try to crush them so that the oil permeates the sock then rub the pot with it.
I think you will find that it is probably not calcium (due to the lack of effect the CLR had) but in fact fertiliser salt deposits. Usually this accumulates from chemical fertilisers which is a good reason to stick to organics. I have some on a few of my pots and its very difficult to shift. I will have to give the burying method a go and see how that works out for me. Cheers for the interesting post,
Joe
Oh and one more quick question, It appears that from the pictures that the patina has been reduced somewhat. Is this the case?