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It is interesting to see all the different types of materials possible to be used for watches and what the difference are. For example, Rolex fans can go on and on about the benefits of the particular stainless steel, 904L, Rolex uses for their cases versus the typical 316L most others use.
Yup, to be clear, what the manufacturers and suppliers call lead free (I called it 'no lead' in my post above) does not mean 99.999% Lead free. Lead is considered a contaminant for the most part in alloys with less than 1% Lead, and due to the raw materials, including scrap copper alloys, used to make the alloys, it can be much more expensive to achieve lower lead levels. Also, the benefits of Lead, easier machining, improved fluidity during casting, corrosion resistance, need to be rejigged with a new alloy system that does not contain a significant quantity of Lead.
Copper.org has this to say regarding Lead in copper alloys for potable water sources:
"The 1986 Safe Drinking Water Act (SDWA) amendments included Section 1417. This section addressed concerns for lead contamination in drinking water systems. As of June 19, 1986, all pipes, solders, pipe fittings or plumbing fixtures used in the installation or repair of any public water system or any plumbing in a residential or nonresidential facility which provided water for human consumption had to be "lead-free." The term "lead-free" was defined to mean that solder and flux could not contain more than 0.2 percent lead; pipes and fittings not more than 8.0 percent; and plumbing fittings and fixtures must comply with voluntary standards required under the SDWA."
RG7, C93600, is consider a low lead alloy and would meet the above requirement if it were used in potable water systems. B-Metal, Red Brass, C836, is often used for water works castings (around 4 to 6% Lead).
Recently California changed their rules about Lead in potable water systems:
"What are the maximum allowable lead limits in plumbing products?
Before January 1, 2010, the maximum allowable lead content in “lead free” pipes, pipe or plumbing fittings, fixtures, solder, or flux is as follows:
0.2 percent lead in solder and flux;
8 percent lead in pipes and pipe fittings;
4 percent lead by dry weight in plumbing fittings and fixtures.
After January 1, 2010, the maximum allowable lead content in “lead-free” pipes, pipe or plumbing fittings, fixtures, solder, or flux intended to convey or dispense water for human consumption through drinking or cooking is as follows:
0.2 percent lead in solder and flux;
0.25 percent lead in wetted surfaces of pipes, pipe fittings, plumbing fittings and fixtures, as determined by a weighted average."
Given that the Bronze cases will hardly be in contact with the skin (as the case back and buckle will be in stainless steel) the actual amount of Lead in the Bronze case is of little concern to the end consumer, unless someone decides to eat it.
Keep on with the Bronze watches, they are looking great so far!
Lukas