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.
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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