I bought a small bottle of Tung oil (low gloss). I decided not to use it for a current project after calling the company for info on it's properties. Why use Tung instead of Blo, or mineral oil, or other oils? I'm wondering if they are interchangeable enough that there's no need to stock/use different products. I know about the need for "food safe" products like mineral oil, etc. But for non food items, why does one guy swear by Tung oil, while another is content with BLO? I could see ZERO difference between mineral oil and Tung on walnut or maple.
Tung v. BLO BLO faster cure Tung non-ambering Tung better filling properties (I have heard) because thicker Tung pleasant and not overly strong smell Tung no heavy metal driers (Pure Tung v. BLO) Tung more expensive
Tung and BLO will polymerize, while mineral oil will not.
I don't recall the place I read it, but it was some government thing (and you know you can trust them) that once cured, any finishes are considered food safe. I'm not a chemist so I can't tell you what happens to the driers. They are catalyst and evaporate to my limited knowledge.
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.
Good information, but I would take exception to the scare over cobalt. It's a little known exotic sounding element, so it must be toxic, right? Not necessarily. I am a chemist and I worked for three years testing drinking water for EPA regulated contaminants. Last I heard, there was no maximum contaminant level regulation for cobalt and only recommended concentration goals for manganese. Neither are acutely toxic in the same sense as some other so-called 'heavy metals' such as lead, mercury, cadmium, thallium and arsenic. The term heavy metal is an artifact of the media as far as I can tell, and was never mentioned at any point in my long, grueling years as a chemistry student. There may have been some cases of industrial workers being debilitated by breathing large amounts of the dust, but similar health catastrophes can happen with coal dust (black lung), rock dust (silicosis) or even wood fiber dust. I have heard of other health effects like enlarged thyroid with cobalt and restricted iron uptake with manganese, but exposure levels must be hundreds of times what is normal in food and water over a long period of time. Both are essential minerals for the maintenance of life and probably have much the same function in our bodies as they do in oxidizing finishes as catalysts. Too much of just about anything can have adverse health reactions including calcium and some vitamins.
So let's do some math on what we might be exposed to using a salad bowl finished with something that contains these driers. 0.25% = 2500ppm (parts per million). If we use 1/20 of a liter of finish for our bowl and assume that the density is about 80% that of water, then our bowl has about 100mg of combined cobalt and manganese in its finish. If we further assume that only 1/2 the surface is food contact area and we consume 0.1% of the finish with each use, then our exposure to combined cobalt and manganese comes to about 0.05mg per meal. That would be approximately the same as drinking a liter of good quality treated water, with the additional point that neither of these metals is regulated with a maximum contaminant level from the US EPA. Conclusion: intake of cobalt and manganese from food contact items using finishes containing these driers would only be a fraction of normal intake from food and water. We all have much bigger fish to fry for improving our health than this.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.