Miscellaneous

Advice on Hydrochloric Acid

Excerpts from letter from Lucy Talcott, September, 1947

For correcting effect of too much acid (a hairy look which appears some months after washing and which continues into disintegration): soak objects so affected in water for two weeks, changing the water every day.

"It is my impression that the precise proportion of hydrochloric in the washing bath may not matter too much. After all, the things are only dipped in for a few instants - never left in, but dipped in, in a strainer; and the acid must be just strong enough to bubble up nicely and get after the incrustation. The thing that matters is the soaking afterwards - after the pieces are brushed and rinsed - in at least two changes of fresh water."

"With respect to the acid, Andreas was rather hard to pin down, and assured me that he always used his judgment, and the proportions had to be analogous to the object ..[handwritten: ✓]

"However, it developed that the canonical proportions are considered here to be three parts water to one acid. This may be varied up as much as half and half acid and water, and sometimes even more acid than water, if the stuff does not clean up with the 3 to 1, and if the pottery is hard and has no added color etc.

"On the other hand, for very fussy stuff it may be used much weaker, and, as I said, the things just dipped in for an instant, then washed a little with cotton, and rinsed.

"It seems that on some of our terracottas, where there were good remains of color, but the things didn't clean up easily with water, he has used a little acid - contrary to instructions, but with excellent results .. On such he has experimented with a paint brush or cotton on a small area before proceeding with the whole.

"I cannot see that Mr. Penderleith has any use for an acid solution stronger than 5 percent, but this seems to relate not at all to our activities. I wonder though if his remarks about the salt content of the soil may have any bearing on your problems ? ?