refractive index of Oil paint samples by manufacturer, does it exist?ApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2018-06-28 22:45:16 ...
Most recent comment 2018-07-01 14:59:35
Oil Paint
Paint Making
Pigments
Scientific Analysis
If it is not available, I would like to make a database of the refractive index of Oil Paint samples, along with their partical sizes per a given unit of paint, for each currently available, and respected oil paint manufacturar.
Is this information which has already been collected? If it is, I would really appreciate information on how to access to the data.
I am not sure how to catagorize this question.
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Moderator Answer
(brian baade)
I know of no such database mainly because what you propose is incredible
complicated and in some ways not meaningful. When you write the refractive
index (RI) of a paint sample what exactly do you mean?
This is a great article on RI and transparency/opacity in paint:
https://www.naturalpigments.com/art-supply-education/transparent-opaque-paints/
RI describes the speed that light moves through a material as compared to
the speed it moves through a vacuum. This becomes important when light moves
from the interface of one material into another (how light bends). There are
multiple RIs in a given paint. There is the RI of the oil or mixture of oils.
This is easy to identify, at least initially as the RI of oxidized drying oils
increase slightly over time. Each pigment has a specific RI (actually many have
more than one, depending on particle shape and other factors). To this, you
then add the RI of any stabilizers, like aluminum stearate, etc. The closer the
RI of the various components, the more transparent they are in each other. This
why lower grade cadmium paints that contain a high proportion of low RI aluminum
stearate are inherently more transparent than those that contain little or
none. In paint, we are interested in the effect of one or more RIs in a matrix
of another. In essence, paint is a mixture of RIs, all of which would
contribute to a paint of a certain transparency/opacity at a given thickness.
This is not the same as a RI for a given paint.
As to particle sizes, many pigments come in different grinds to maximize for
different effects or for specific reasons (greater transparency for glazing,
etc) so just knowing a pigment number would not always be enough to discern
this info. Also, I would guess that manufacturers have records of the particle
sizes and morphology of each pigment they use for each specific paint in an
effort to maintain consistency from batch to batch, but it is certainly not
common knowledge and is unlikely to be easily obtained.
Please let me know if I somehow missed the point of your question.
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