[TheForge] Other thoughts on: oil/wax finish, blackened steel
Cheryl Brimson
cbrimson at me.com
Sun Oct 24 18:24:34 EDT 2010
Bruce:
I agree that you would not want to use linseed oil on anything that will come into contact with food, but it does make for an easy to use renewable finish, if it wears off. If being food safe is the main criteria for finishing the piece I use either the olive oil from the kitchen that I cook with, or bowl turner's wax, which is primarily beeswax blended with paraffin. I keep a tub of it around for treating the wood bowls we have and the cutting boards. If you want to be picky about it, I would argue that using metal scale as a component of your finish for something that will come into contact with foods not a really great idea either. Low carbon A36 steel used for most general smithing contains not only iron, but trace amounts of carbon, manganese, silicon and phosphorous in the form of oxygen free copper. Other alloys contain chromium, nickel, tungsten, vanadium and other heavy metals. Like most blacksmiths today, I rely by both examples of other smiths and by research into current and past practices. In my experience, you use the process that suits what you want to achieve, and don't try and use what is not appropriate for the particular job at hand. A lot of patination processes do use particularly hazardous ingredients (arsenic, copper sulfate, chromium oxide, sulfuric acid, just to mention a few) and you have to be extremely careful when using them or you can injure your health irreparably. They do have their place however, as a means of obtaining a particular look, and should not be ignored.
I personally do not forge much in the way of food related metal items. Most of what I make falls under the heading of small artistic items or tools. A lot of what I finish has to be treated so that it will not rust readily and what I have been making for outside applications gets treated with Permatex 79DA Rust Treatment, which contains phosphoric acid. I use a wire brush and then give the metal three coats while it is still warm off the forge. I let the warm (several hundred degrees) steel bake the first coat into the metal and when it dries, and place it off to the side on the forge table to keep it warm (not hot) and then give it two more coats. If it is necessary for the steel patina to show, I then spray it with a clear acrylic sealer. If it is going to be left outside, I give it a couple of coats of a good satin finish black enamel.
Regards,
John
On Oct 24, 2010, at 8:40 AM, Bruce Freeman wrote:
> As noted in above replies, Japan drier does contain metals, possibly
> including cobalt. See the Wikipedia article or MSDS sheet (for a
> particular product) for details. I cannot comment on Brimson's
> assertions about the degree of hazard these metals pose, as I am a
> chemist, not a toxicologist, but, it is a given that one does not use
> "boiled linseed oil" (containing Japan-type driers) on food-contact
> articles.
>
> In the latter regard, let me repeat what I've said many times on this
> forum: Linseed oil is not a whit better (and it is a LOT more
> expensive) than any other polyunsaturated oil when it comes to HOT
> finishing an iron article. Develop the scale on your piece by heating
> to red and cooling to black. Apply polyunsaturated (cooking or salad)
> oil when the iron is hot enough to smoke the oil a little, but not a
> lot. Or, apply a thin coating of the oil to cold, black iron, and
> bake at 350*F-400*F for an hour. A very nice, shiny black finish
> results. This is exactly the procedure used for "seasoning" cast iron
> cookware. It provides some protection from rusting, but will not last
> long outdoors. What it is, really, is a dark brown dried oil over a
> black scale. If you put an oil coat on shiny steel, it will look dark
> brown (which usually is not what you want).
>
> So, what I proposed in an earlier post is an experiment I've yet to
> try myself: Add firescale as pigment to the oil and apply it hot.
> Carbon black would work for sure as such a pigment, and is suitable
> for stove blacking (which is mostly carbon black of one sort or
> another), but might leave an undesirable "marking" surface to some
> objects. Fire scale is MUCH harder and less likely to mark. But this
> idea is yet untested.
>
> By the way, I consider the key ingredients of stove blacking to be
> pigment (carbon) and vehicle (oil). Turpentine is to thin the mix,
> and is irrelevant and undesirable if it is to be applied hot. Waxes
> might provide a harder surface, or a shinier one, but I doubt it --
> the baked oil is fairly impervious and quite shiny. Think "dried oil
> paint" to get the image.
>
> And as long as it is understood that polyunsaturated oil must be baked
> to set properly, then there's no need at all for Japan drier in the
> mix.
>
> Another aside -- Carbon compounds themselves can be quite toxic, and
> "carbon" from unknown sources may contain oxygen and nitrogen in its
> chemical constituents (to say nothing of outright contaminants) that
> increase the likelihood of toxicity. Pure graphitic carbon is safe
> because your body would never absorb it, but a black compound could
> contain anything and probably does. (Lampblack, for example, is a
> suspect carcinogen.) If you really wanted to assure the safety of an
> unknown carbon black material, you'd have to take some considerable
> trouble with it.
>
> Activated (baked) charcoal is probably the safest by far, as its
> origin is known and the activation process drives off most of the
> small molecules. (Activated charcoal is sold at the drug store as an
> antiflatulent, and is often used to absorb other ingested poisons.)
> Activated charcoal is the only "black" I would suggest you ever add to
> anything that will be in contact with food. There may be other safe
> "blacks", but I don't know them. All this worry is probably
> excessive, but since the potential toxins are so easy to avoid, you
> might as well know about them.
>
> On Sun, Oct 24, 2010 at 12:05 AM, Cheryl Brimson <cbrimson at me.com> wrote:
>> If you have any questions about toxicity, do what I've done for years, check the manufacturer's MSDS sheet. All products, especially manufactured chemicals, have to be able to show what active ingredients and physical/physiological characteristics they possess. I looked up the MSDS for Dynamic Mfg.'s Japan Dryer and Boiled Linseed Oil, and you have more toxic products in either spray paint/polyeurethane varnish or paint remover. I have known a few people who suffered from acute sensitivity to cobalt from grinding carbide tool components in progressive dies, but that degree of sensitivity is rare. The fumes from using arc welding rod or the scale you wire brush off forged steel is probably more harmful; as is the dust from the coal or coke used to forge with. The key is to use a mask to contain the dust and to have adequate ventilation. Use gloves to protect your skin from contact dermatitis and you are probably fine. FYI dryers or accelerants for oil based finish produc
>> ts generally do not contain "solids" but are "thinners" such as gum turpentine or isopropyl (denatured) alcohol. All of which is fine, unless you are going to try to drink the stuff. Keep a bottle of Scotch or Captain Morgan on hand for that.
>>
>>
>>
>>
>> On Oct 23, 2010, at 10:20 PM, Mike Spencer wrote:
>>
>>>
>>>> ...I've been warned that the dryers in "boiled linseed oil" and
>>>> japan dryers are capable of giving you heavy metals poisoning...
>>>
>>> I think (but can't immediately confirm) that "Japan drier" has become
>>> a generic term for several kids of drier. Cobalt is used in several
>>> brands of driers. In addition I've seen an allegation that "boiled"
>>> linseed oil contains "arsenic, beryllium, chromium, cadmium and
>>> nickel" as drier constituents. Bleee.
>>>
>>> Years ago, a smith here called the makers of a brand of boiled linseed
>>> oil sold here and asked about using it on food prep utensils. The
>>> company rep emphatically urged him not to do that, but to use "raw"
>>> linseed oil. The rep confirmed that "boiled" isn't boiled but has
>>> driers added.
>>>
>>> So I just stay away from "boiled" linseed. For a railing or exterior
>>> paint it's probably fine but why mess around?
>>>
>>> - Mike
>>>
>>> --
>>> Michael Spencer Nova Scotia, Canada .~.
>>> /V\
>>> mspencer at tallships.ca /( )\
>>> http://home.tallships.ca/mspencer/ ^^-^^
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>
>
>
> --
> Bruce
> NJ
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