On Thu, 09 Jun 2005 19:59:28 -0700, David wrote:

Even oils with metallic driers?

Which metal ? What's "food safe" ?

A few decades age we had a reaction against lead-pigmented paint in
childrens' toys. Now that's a pretty sensible reaction -- 20%-30% of the
paint might be a lead pigment, and they're getting chewed.

For oil though, the drying agent is about 0.25% and it's likely to be
used on items where the finish is left undisturbed (barring marauding
chinchillas). So even lead-dried oils are nothing like the toxicity
hazard of pigmented paints - however the upper lead limit on a saleable
finish is something like 0.2%, so they're still forbidden.

Lead oils (for centuries) were usually a mixture of lead and manganese
driers, as this gives the best resultant oil. Shrinkage is reduced and
they dry in all weathers. When lead fell from favour, the first response
was to simply omit the lead and use manganese alone. The problem with
these is that they need a dry climate to cure and will remain
perpetually sticky on the surface if used in Wales or Seattle. They're
also too inflexible to be used on oilcloth, and have some tendency to
shrinkage cracking.

The modern replacement for lead was cobalt. This is an effective drier,
although the resultant finish isn't as robust as a lead-dried oil. We're
recently starting to see toxicity concerns over cobalt too - the element
itself is regarded most dubiously, although I haven't heard too much
concern raised yet over its use as a drier.

As a general finish for furniture, the only linseed oil I use is either
raw or lead/manganese dried. I don't much like either as finishes, so I
only use them on repro work - I make the lead-dried oil myself. For
most work I'd rather use tung, and avoid the yellowing. As toxicity is
concerned though, I don't much worry about either - I wouldn't use them
as a finish for kitchenware or toys, but furniture is no significant
risk.

--
Inbreeding - nature's way of always giving you enough fingers to count your cousins