MITRA Forum Question Details

There are a lot of different materials listed in this inquiry  so I am going to start by distinguishing between traditional artist's oil primers and architectural primers. Utrecht Oil Priming White, which the OP mentions, is not an alkyd-based primer. The binder for this product is a combination of alkali-refined linseed and safflower oils, not alkyd. Alkali-refinement is totally unrelated to alkyd, despite the similar sounding terms. Alkyd is a resin synthesized from vegetable oils which produces a tough, fast-drying film. Alkali refinement is a process of "washing" away free fatty acids, mucilage and other components of expeller-pressed oil. (Expeller pressing extracts more oil from flaxseed than cold pressing, but it also releases additional material that would make the oil less usable and prone to spoilage if not removed through refinement.) So, a paint that has alkali-refined oil as a binder has a vegetable oil binder, and the product is a traditional oil paint. Oil-priming white has a very high proportion of solids (white and inert pigments) and is not brushable from the container like a house paint-type primer. 

Silicone alkyds are a type of solvent-reducible paint that has superior weather resistance to older types of alkyds. Urethane alkyds are a hybrid product that facilitates water cleanup instead of hydrocarbon solvents. I am not knowledgeable as to whether these types have any application in permanent painting, but architectural paints are not generally formulated for durability into the antique age as we expect (or hope) paintings will achieve. This isn't a defect- it's expected that buildings will be repainted every couple of decades at least, so house paint can have components that aren't normally used in artists' paints, if the ingredient imparts a desirable performance or appearance and does not need to last "for the ages".

"Enamel" is a generic term describing the shiny, hard, level finish associated with this type of paint, and the typical applications, like vehicle exteriors. Most enamels are now alkyd or acrylic-based, but in the past, natural resins were used instead. "Coach enamel" was once made from Congo copal or other natural resins, heated and mixed with dangerously hot oil. 

The last part of my response deals with the question about bulk commodity ingredients like whiting or "marbledust", whether there is a difference between brands/sources, and whether the difference in price reflects a significant physical difference in the product. This is a broad question which is not going to have a single answer for every product. I can confirm, however, calcium carbonate sold for artists as a consumer packaged product has been recalled if found to contain asbestiform particles. I assume that there are some industries where this is not restricted, so that is one commodity I am confident in saying that artists are getting a higher grade compared to industrial or bulk supplies.