Sealing Very Old Moroccan Iron

Try a matte finish acrylic, or other, coating.

Remember, rust never sleeps, so you may have to re-coat, if left outside.

Dupli-Color/Matte clear coat Paint Shop finish system (BSP307 ...
Dupli-Color Paint Shop Finishing System Clear Coat Matte Finish ...
Clear Coat Spray - RustOleum.com

A couple of links for your info. Http://www.innate.com/Paint/Chrome/glamour.htm http://www.hotrodders.com/forum/good-quality-clear-resonable-price-229444-2.html Good luck!

I've specialized in artifact preservation so I'll sit this one out

What color are you going for? Ospho (phosphoric acid) will leave the finish flat black and tight if you chip it a little. It converts the iron oxide to iron phosphate. http://www.ospho.com/directions.htm

You need to describe the sealing conditions, or we can't be of much help. If it's a dust shield, it's simple. Pressure, temperature, and fluid or gas parameters are requited.

Try this: For an object that you want to preserve, but not restore, I have used a clear coating after using solvent for removing grease and brushing off loose rust and dirt. I started with Penetrol, a paint additive, but it went bad in the can since I used so little at a time. Now I am using varnish, which so far is doing OK. It darkens rusty areas, but brightens painted areas. (I liked Penetrol better, except for gelling in the can.) It appears to protect the surfaces from further deterioration--at least when kept inside in a non-heated building. The secret seems to be to put it on with a cheap brush or even a rag, then wipe it off after it can penetrate a bit, but before it dries. (Makes for sticky hands.) I have even wiped off with paper towels. By wiping off the gross amounts, it does not dry shiny like it has been painted, instead it preserves the patina that I expect you want.

I have had very good luck with artists varnish, usually used for paintings. They will seal things in for a few hundred years.

Spar varnish would also work, the first coat should be thinned to watery texture, and let dry well between coats.

Though I use clear lacquer on my art metalwork pieces, but only because it is so easy to fix when it scratches.

(usual disclaimer)

If you want to seal the rust from further rusting you need a product that wont breath. Most varnish will breath. The best I have found is a product called Por15. It will seal, and the product can be left outside without further rusting.

I do not want to . . . allow the finish to show in any way.

I assume that this statement means that Migo-1 does not want the finish to show; that is, it should not be shiny even if the finish is clear. That is the same thing I want, which is why I suggested my experiments with wiped-off clear finishes. Perhaps it won't be "sealed," but it certainly offers some protection. We do not know if it is to be stored outside.

I have never used POR15, but have certainly heard of it. I don't even know offhand if it is clear.

Try POR-15. Used it on my 1973 Porsche 914 right over the rust in the battery holder area which 914s are prone to. Work very well.

UFG