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Proven solutions to the problem

Posted By: John Morris (70.108.168.139)
Date: Saturday, 13 June 2009 1330 hrs. EDT

In Response To: What's happening is pretty clear (John Morris)

In case you didn't read my postings on this subject ca. August 2008, my informal survey (I can't quite call it a study) came up with some proven solutions to the outdoor bronze cannon corrosion problem.

1. Move corroding cannons indoors.

Informal Trials conducted:

a. Springfield Armory moved their French ca. 1760 bronze 4-pounder indoors ca. 1970's. The weapon looks like new, with no evidence of corrosion whatsoever. I posted photos of it previously. The current S.A. staff does not have records of the piece having been cleaned, but it looks to me as if it may have had some gentle cleaning since the surface has no evidence of corrosion whatsoever, and that would be quite rare for any bronze cannon kept outdoors for any length of time.

b. Watervliet Arsenal Museum moved most of their bronze cannons indoors sometime during the mid-20th C., maybe 1950's from what I recall hearing. Many show evidence of past corrosion, but it was stopped in time to prevent major damage to the markings in most cases. There does not seem to be any corrosion in progress since the pieces are not exposed to acid rain or direct sunlight, two things I've theorized work in concert to attack old bronze.

2. If cannons cannot be moved indoors, do a cursory cleaning by approved methods to remove only the loose corrosion products, then dry the entire piece thoroughly using heat if required, and seal all surfaces using opaque, waterproof paint. To make this method fully effective, the inside of the bore must be included in the drying and sealing so water can't get under the sealant. Plugging the muzzle with waterproof tompion may be required. The vent must be plugged also, suggest inserting a slightly oversized lead projectile such as a .22, using a punch or drift. I added the words about cleaning and drying for good measure, since all I can be sure that was done in the following cases was the painting.

Informal Trials Conducted:

a. Ft. McNair, DC. A pair of French 4-pounder guns was painted black sometime after I photographed them in the mid-1980's. As of July 2008 the black paint remained and no evidence of corrosion was observed. I was unable to find anyone who could provide details of who painted them or when, or what if any cleaning or drying was done at that time. However the surface of the bronze, deprived of both moisture and sunlight, appears to be stable from what I can see since the paint isn't cracked or disturbed in any way.

b. National War College, DC. A pair of large bronze cannons on the steps at the entrance was painted gold at sometime after my mid-1980's visit. These are not doing quite as well as the black-painted cannons mentioned above, since it appears that moisture is getting under the paint somehow, or the cannons were not dry when painted. Some of the paint near the breech was broken open by expanding corrosion products. However these are isolated areas and the large remaining areas appear to be stable with undisturbed gold paint.

c. Washington Navy Yard. A small bronze cannon of unknown origin has been kept painted black ever since I've seen it on outdoor display (I'm guessing since about 1982.) The reason it is painted black is that it is displayed among a number of iron cannons which are also painted black. There is no evidence of ongoing corrosion on this piece.

d. U.S. Naval Academy, Annapolis, MD. A small Spanish bronze cannon displayed outside near Ward Hall has been painted a dark green color since probably the 1920's. It is always painted that color because, like the item described in (c) above, it is among other iron or steel items which are always kept in dark green paint. The marks on this cannon, such of them as are visible through the paint anyway, appear sharp and undisturbed, and there does not seem to be any corrosion under the paint. However only stripping paint will allow a complete examination, and I've recommended that this be done under laboratory conditions to fully document the condition of that piece.

Again, photos of most of these cannons are included in my my 2008 postings on this topic.

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