Using a shellac is the way it was done years ago. It has fallen out of popularity. As stated it yellows and flakes off. The rustolem, or oil will penetrate the pores and help seal it aginst moisture.
privy you said you had put WD40 on it already, you'll need to get it off before you paint it if you go that route. Here's a grenade that was done in shellac.
There's some good conservation resources online from, I believe the Texas A & M Marine Archeology Dept. They have a manual you can down load. Some other ideas on your cannon ball, here's what I've used. My reverse electrolysis usually takes months since the objects were in salt/brackish water for years. Since you've already done that I'll skip it. After the object is taken out of the electrolysis I boil it for about an hour with a couple of water changes(this help draw more salt out). Then put it in an acetone bath for about a week covered (the acetone will penetrate deeply and bind with the water to help it evaporate quickly once taken out). I then take the object out and put in in the sunniest location possible. I let it dry for a day then brush the whole thing with "Extends" rust converter from Loctite. After that is dry it should leave a nice dark color. I then seal with semi gloss polyurathane. At this point you could leave as is or spray paint with black paint. Hope this helps.
P.S.- Since you've already wiped it down with WD-40 I'm not sure how well paint will stick now.
Jay
I only wiped it down didn't give it a bath so to speak. It has already dried pretty good. I'm going to see what the local historical society wants before I do anything.
here's some better pics several hours after the big clean
As you can see the WD-40 didn't even penetrate some of the pores in the shell.
I don't think any more electrolosis would do any good...what do you think.
I like the idea of black with white painted C.W. BORMAN on it.
Did you dry it in the oven? You gotta get the moisture out of shell. Just air drying ain't gonna get it. Hit the threads with a stiff wire brush, they shoud clean up a bit more. The inside needs some more work. It's a little rough I thought it clean some what better, not as many pits. It must have been wet or damp from where you recovered it.
I'd leave out C W most people wouldn't know what that was. Just another suggestion
U.S. 12 Lb. Borman (fuse missing)
1861-1865
place where you found it, and maybe a date
For a base to keep it from rolling around see if you can get a piece of 2 inch or 2½ ABS plastic pipe about an inch high should do the trick.