Q & A: A few bronze care basics
Q: What would be a safe paint stripping product/method that will not harm the bronze? What methods are best to polish the stripped surface? Although polish is not the intent as the casting should be a natural "sandy" texture I believe they would want to achieve. I would be looking for ideas to maintain this texture without having to sandblast, yet get the surface completely clean. Should a clear coat be applied to reduce maintenance needs? What product is best for clear coat protection?
A: If I had my way without restriction, I would use a low grit aluminum oxide to blast the piece. That is what I use to prepare nearly every bronze piece for patination. You could also use any kind of readily available solvent based paint stripper without damaging the bronze. However, I imagine that would be more labor intensive, and I'd be skeptical as to how well it would work. The aluminum oxide approach will also help to restore the natural sandy texture of the casting.
You mentioned that the spec required color to be equal to patina. Now, I'm not sure of your particular situation, but it sounds like you are working under the assumption that the client thought that the piece was painted a "faux bronze". It seems like that is what you are thinking "patina" is in reference to. You may be correct, but I just wanted to mention that in the bronze casting industry we use the word patina to represent a change in the surface of an otherwise "virgin" bronze casting. When clean, most modern bronze alloys have a "goldish-red" hue. The look associated with bronze that has been introduced to the market has been created artificially in almost every instance. For example, at the very least a bronze piece has been oil rubbed or "antiqued" by applying a darkening chemical and then scrubbing the chemical back so that the highlights come up "goldish" and the recesses stay dark. In other circumstances, chemicals are applied to make the bronze piece turn to more of a brown/honey brown/ red-brown and of course green. I am only mentioning this to you in case an actual patina might be required before sealing. If the intention is to keep the bronze in it's restored state, then the traditional method for sealing is to use a microcrystalline wax. The wax is applied then buffed. However, that will only protect for six months or so in the elements. If you want maintenance free protection for many years, there is a great lacquer you can use called Permalac.
The original question and answer can be found here.
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Inspired Bronze