Concern re driers causing possible darkening in oil paints made with semi drying oils? ApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2017-08-21 04:03:00 ...
Most recent comment 2017-09-05 10:16:48
Dear MiTRA person
I recently purchased some oil paints by a reputable German manufacturer who sadly is not explicit about the oils used as binder. They admit to using a combination of oils but the feeling on online forums is that there is probably a preponderance of safflower or perhaps even sunflower oil. I have some concerns about using them because inevitably they must have added some driers and I am given to understand that some metallic driers like manganese can cause darkening in the paint film over time. As is noted here in the resources articles, most paint manufacturers do add driers to one degree or another but the devil is of course in the detail ie how much? I've emailed them to enquire as to whether they have done any testing or have any reassuring information on this front but the response was a bit confusing as they kept directing me to information regarding the lightfastness of these paints. (And by the way they use the Blue Wool scale to assess lightfastness which as far as I know is very outdated!). Do I need to be concerned regarding darkening when using paints of this type?
Answers and Comments
Having very little information on which to base an answer, I would guess that a "combination" of oils means a more neutral-colored vehicle was selected for whites. If these are professional-grade, manufactured oil colors, I would assume driers are added in very precise, laboratory-tested proportions calculated by paint chemists. At least, that's my experience with paint manufacture. Exact formulas for oil paints are
often held as proprietary secrets, though it strikes me as unusual
not to disclose at least generally which oils make up the vehicle.
Many manufacturers (Utrecht included) select oils other than linseed for pale colors and whites. The use of neutral-colored oils for whites is not experimental or exclusively modern- the practice dates back centuries in the Northern tradition and is mentioned in manuscripts including William Beurs' treatise. While arguably not the equal of linseed oil, safflower, poppy and walnut oil (all similar in ratio of linolenic to linoleic acids) are still considered proven paint vehicles suitable for permanent painting. Sunflower oil is available with different fatty acid ratios, so I wouldn't make any assumptions as to general suitability based on food-grade oils- if sunflower is being used, it may be a type that is better for painting than for eating.
The Blue Wool Standard lightfastness test is a good method for the artist to conduct in-studio testing of colors. It's not up to the ASTM D 4303 standards, which are more rigorous.
Personally, I don't see any reason why a paint maker would not disclose what specific oils are used in a given color, barring some tiny amount of a proprietary ingredient. Nevertheless, where listing of the exact vehicle is concerned, as I understand it, under ASTM D 4302, where multiple oils, resins or gums are used in multiple colors across a paint line, it is permissible to include all possible on a given label (e.g. "Alkali Refined Linseed or Expeller Pressed Safflower Oil"). Compliance with ASTM D 4302 is voluntary, however.
It's important to note, BTW, that ASTM D 4302 actually prescribes the minimal use of driers for slow-drying colors that would not otherwise meet the standard for acceptable drying rate.
I cannot speak to the exact oil mixtures in the Norma paints.
I hope that in near future that we can have a technical
contact at Schmenke to help answer questions like this.
The paint industry does not, in general, give exact formulations, but a list of
the major ingredients. This can include precise materials like (eg walnut oil)
or less precise (eg mixtures of selected drying oils) while most will give the
exact pigments included in their paint. They almost never give exact amounts of
small additions of stabilizers, driers, etc. Modern fine art paint manufacturers
likely add different amounts of driers to each pigment oil mixture (especially
in their professional lines) to moderate and help to equal out the drying across
the entire range, not just a single percentage for all paint.
As far as drying oils, please refer to our section on this
subject in our resources section. The only one that you mention that concerns
me is sunflower oil. Yes, Sunflower oil is available with different fatty acid ratios. However, there have been some examples where professional oil paints were made with large
amounts of sunflower oil and these have exhibited major long-term drying defects. Yes, these were probably made with an improper grade of sunflower oil but I can see no advantage in its use at all other than its extreme economy.
Brian, according to my experience, you're correct- each color in an assortment is individually formulated, and siccatives are applied according to the characteristics of the pigments used.
Sorry, I intended on wrting drying.
The problematic paints were formulated with sunflower oil.
You may want to write the manufacturer and ask about this.
I am sure that some, or even a lot, of testing is performed
before the products are brought to market.
My opinion, however, is that even greater transparency about
ingredients and materials would only make everything better and give those
customers that care more info to guide their buying
decisions. Additionally, it could help differentiate lower and higher
quality of Artist's or Professional grade
paints. The terms today appear to be rather nebulously used
beyond pigment choice.
I agree, there's really no good reason to be vague about the general composition of an oil paint vehicle. If artists are curious enough about your products to ask for detailed information, it means they are very interested in using them. Having specialist craftsmen talking about your products is an advantage you can't buy or conjure up, and when it happens, it's a good idea to make yourself available!
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