lead lead everywhere

December 21, 2007 11:30 AM

California has a new law that specifies limits for lead in jewelry products. Even though the answer to my question should be a no-brainer, I need to confirm:

In the text of the law, specifically section 3.2.2, it says that "Class 2" plated metals should be made of metal alloys that contain less than 10% lead by weight ("88 metal").

Then later in section 3.2.2.2 it talks about plastic or rubber materials needing to contain less than 0.06% (600 parts per million) lead.

Does that mean the 10% translates to 600,000 parts per million lead?

That is, if 0.06% = 600 PPM, then 10% should = 600,000 PPM. Correct? It just seems like a huge difference.

posted by edjusted to science & nature (10 answers total)

10% would be 100,000 PPM.
posted by rancidchickn at 11:32 AM on December 21, 2007

1 million * (0.06%) = six hundred
posted by yeoz at 11:38 AM on December 21, 2007

Er, 1 million * (10%) = one hundred thousand
posted by yeoz at 11:40 AM on December 21, 2007

Oops, sorry, really bad math on my part. Yes, I meant 100,000 PPM.
posted by edjusted at 11:41 AM on December 21, 2007

Ok, so it *is* just a simple straight math conversion. There's no "trick" to converting between % and PPM?
posted by edjusted at 11:42 AM on December 21, 2007

Keep in mind that 10% = .1 and 0.06% = 0.0006.
10% is ~166.667x larger than 0.06%
posted by yeoz at 11:43 AM on December 21, 2007

Yes. Straight math, more or less.
posted by yeoz at 11:44 AM on December 21, 2007

Thanks yeoz. Yes, I'm reading "ten percent lead by weight" as meaning 10% = 100,000 PPM. The law actually spells out that "0.06 percent" is 600 PPM so I'm good there.
posted by edjusted at 11:58 AM on December 21, 2007

Per cent is literally "per hundreds". To convert from per hundreds/% to per millions, multiply by 10,000.

The difference between the regs you're seeing is almost certainly to allow pewters to remain on the market, while banning lead in paints, pigments and plasticisers.
posted by bonehead at 12:05 PM on December 21, 2007

I just found this while researching my own lead question and thought I'd be anal and point out that parts-per-million is not the same thing as "by weight." What you're doing is similar to comparing a measurement by volume to a measurement by weight (but ppm is neither volume nor weight). So your numbers are going to be a little bit off, but the difference is as vast as you think it is.
posted by winston at 7:24 AM on July 16, 2008