Why use Tung oil?

[Baron]

You are absolutely correct about the relatively small quantity of cobalt exposure. The reason the EPA has no limit on cobalt in drinking water is that it has not been recognized as a problem. At least, not yet. It seems like every year, another limit is placed on some contaminant, for good or bad. The term "heavy metal" is a really soft term that was applied to just a few metals many moons ago. Since that time, it has come to mean anything on the Periodic table that is left after chopping off the appropriate groups like halogens, alkali metals, etc. As a result, the term includes so many metals that it is essentially worthless.

As for finishes being food safe once fully cured, that is correct. The issue is the term "food safe". That means the finish can be in contact with food. It does not mean that the finish is safe to eat. As was pointed out, lead paint was banned because children were actually eating it. It also happens that lead from various pigments can be leached out when in contact with acidic food so it really was not "food safe". The metallic driers in modern finishes are safe when used in a finish that fully cures and the finish is not actually eaten.

[Australopithecus scobis]

Was mentioned in mine.

[Australopithecus scobis]

Just to add some more froth the the fire: I'm perusing "New Artist's Handbook" (which is really very good). It tells us that "oil-soluble phenolic resins are usually based on a mixture of linseed and tuna oil." So now we have to look for a dolphin-safe icon on the varnish can? :)

Relevant to this and similar threads, I just stumbled upon

which has MSDS pdfs for several manufacturers' products (T&T, Waterlox, etc.)

[Australopithecus scobis]

But excessive use of elbow grease may degrade the finish.

[Australopithecus scobis]

You might be jesting, can't tell. I do use nose grease to lubricate scrapers whilst turning the hook. I have used it to assemble fishing rods. No, you weren't jesting, were you!

[George E. Cawthon]

Fish? If you are a fisherman or hunter, you have much more to worry about, especially if the streams have any contamination from insecticides and herbicides and the fields are sprayed with the same. One fish out of the Snake River or any other river used for irrigation would have a larger dose of any "heavy metal" in organic form than your salad bowl coating. Heck, eating recommendations for Pheasant in some places is down to 1 every 2 week or none for pregnant women.

[Hax Planx]

I don't know of any maximum contaminant level (MCL) regulation that is unreasonable. If a water source has an MCL violation, you can rest assured that the concentrations of that contaminant are very high compared to what is normally encountered with clean water. Concentrations of cobalt are typically in the microgram/liter (ppb) range for clean drinking water, so an MCL regulation would probably be nearer the mg/L (ppm) range considering its low toxicity by ingestion, if such a regulation were ever instituted. It would all depend on what conclusions were on the study that prompted the hypothetical regulation. But what I've been able to dredge up from the Net is that continued ingestion of more than 30mg per day is required to see negative health problems.

A useless media coined term. Gold is heavier in atomic weight and denser compared to arsenic, yet it is non-toxic and inert. There are many other examples. I don't see how manganese at 25 on the periodic table and cobalt at 27 could be considered heavy metals, whatever that means. Of course, Andy Dingley didn't mention that term in his post, but others have in previous threads.

Yes, but in my worst case scenario I wanted to assume that part of the finish is actually ingested. Yet even in this worst case scenario exposure levels were in the microgram range. I think we can forget about manganese entirely since both of the multi-vitamins in my house have 2mg of manganese per tablet, a couple of orders magnitude greater than my worst case scenario. Also the driers are used only in polymerizing finishes and even if small chips of the finish were consumed, it isn't at all clear to me that those polymers are digestible or that the driers could be leached from them. So not only are the driers safe for ingestion, the exposure amounts are at worst small, but quite possibly negligible.

[Noons]

C & M apparently said,on my timestamp of 11/06/2005 10:44 AM:

One of the best lubes for fishing rod sections, in fact. No polymerization, so no sticking.

[Baron]

The EPA tends to overreact to preliminary studies. For example, the recent lowering of exposure limits to methylene chloride is just one example. At least there is some hope that the EPA will actually reevaluate that one.

The term "heavy metal" has been in use way before the "media" could have coined the term. It can be found in all sorts of analytical chemistry textbooks that date back to before the 1940s and was used in the open literature before that time. Way back, it actually did have something to do the with density of a metal but it quickly became applied to all sorts of metals. It definitely has nothing to do with a metal's atomic weight. By the way, gold can be quite toxic when in something other than its elemental form. Just ask anyone who has to take gold containing arthritis treatment drugs. Keep in mind it is not so much the elemental lead that is so toxic, it is what it rapidly turns into in the human body. There will always be certain metals that are way more toxic than others because they severly interfere with the human body's biochemical mechanisms.

I agree 100%. The amounts are so small as to be insignificant when compared to accepted limits.

[Hax Planx]

Yes, but those are some highly artificial organic salts designed to take gold where no gold has gone before. I think it is misleading to compare gold and lead toxicity. There is no comparison. But that is topic drift. I think everybody has too much information now.