Dialogs about physico-chemistry
applied to arts

Chapter II

Emmanuel : If I blend small air bubbles into my paint (let’s figure out first how to do it!), does it have a chance to siccativate faster ?
You know, this question is central in painting, especially nowadays, because painters balk more and more at using heavy metal oxides as "siccative", as oxidants. Note that there is a possible answer with oxidized oils, but their applications are for the moment limited to decoration or industrial use. I don’t really know why. What is your opinion?

Jean-Louis : How to blend small air bubbles into your paint ? By whipping it with a "foaming agent". Does the dough have a chance to siccativate faster? Yes and no. If we talk about oil paint, the paint in contact with oxygen will indeed dry faster. But since the volume of oxygen of a small bubble is low, it certainly will not go very far. And then, the alveolar structure of the paint will considerably retard the later diffusion of atmospheric oxygen. And solvents evaporation. In any case, that is what I think. We should try....

Emmanuel : But what is it, this bubbling thing, this "foaming agent" ? And then by the way, about siccativation, a rough question: why oxygen and not another element?

Jean-Louis : "The foaming agent" is a product that we add in order to obtain very stable emulsions or froths. It prevents from bubble coalescence. For example to extinguish some hydrocarbon fires, the firemen use foam, not water. And they mix some foaming agent with water. Originally, this is a basic soap, like Mir, but you can find specific ones for concrete (cellular concrete manufacturing), for plastics (to make foams), for toothpastes, etc. Opposite, we have anti-foaming agents used for example in laundry detergents. I cannot think of any "basic" product that you could try. I am looking at what I can find....

About your question "why oxygen", it is the only "active" chemical compound of air. Nitrogen is basically inert at common temperatures. Water vapour can play a part for some paints, mostly for « water based » paints, of course.

Bubbles, oxygen and siccativation

Emmanuel : Why, for instance, with siccatives for oil, is it the oxygen that will stick together with double bonds (see Saturation) and not the heavy metal or anything else?

Jean-Louis : For chemical reasons. Some reactions are possible, some are not, and all of them do not produce an “interesting” effect.

A metal will react with an acid to give a salt, with oxygen to give an oxide, but will not make possible the formation of intermolecular bonds. Oxygen, as for it, can be "bridging", i.e. can bond chemically two molecules. Hence its siccativating properties, at least partly.

Oxygen may also work as an activator, the oxidation of two molecules making them reactive and able to bond together. The presence of metals (for instance manganese, in mediums or in siccative like "Courtrai") is often linked to their catalytic effect. They support the oxidation/polymerization reactions without finding themselves captive of the process.

Emmanuel : Why is an element more “bridging” than another one ?

Jean-Louis : This is because of its chemical nature, therefore in fine because of its electron structure. If I go into more detail, it is going to become very technical...

Emmanuel : But which are the elements that you would describe as the most "bridging" ?

Jean-Louis : Well... Actually, it depends on the considered system. If you have already used epoxy glues, one of the tubes contains a resin (a polymer), and the other one contains a hardener. The hardener builds chemical bridges between the resin molecules. In the case of oil paints, it is the oxygen that bridges or helps to bridge.

Emmanuel : All right. But in terms of single elements ?
Oxygen is bridging in oil among others, this is ok, but in some other contexts, can other single elements play this kind of role? I don’t know carbon, sulphur, phosphorus, nitrogen??? But maybe there is not talk of the same structural scales?

Jean-Louis : It is getting definitely chemical and not truly simple. Organic chemistry performs precisely more or less odd and exotic assembling between different elements.

IMPORTANT

These elements are

Emmanuel : Let us go back to soaps. Black soap is quite used in decorative – or even in "artistic" - paint, notably to achieve "distempers" and emulsions (read recipe), but also to clean paintbrushes (passage in Cleansers). I copy-paste for you a quote from a dialog with Anne :

"I put forward a huge hypothesis: black soap would work strongly on esters because it is very alkaline. And not superfatted, my friend  Yes !   We’ll see, but that would maybe explain the existence of common black soaps that are much more loaded in oil (around 50%, can be found in hardware stores) for an ordinary use like floor-cleaning, and nearby, some more "orthodox” versions with 3%."

What is happening with the foaming agent? In which case should it be superfatted? Or be not too fat in other cases? What is that for, according to you, how can an artist deal with these parameters?

Jean-Louis : I am not in the trade, so I do not know a lot about soaps, even superfatted. The main use of superfatted soap seems to protect   pretty girls and babies butt skin. By adding too much fat to soap we will end up with oil paint.

Emmanuel : As a question-like temporary conclusion, if a painter who uses black soap in his paint (cf. for example emulsion recipe) reads this text, he is wholeheartedly invited to tell us why. Is it:

* To saponify oil, a bit like in the case of saponified wax (see recipe), but in a much softer way. The objective would be to get a kind of emulsion.

* To create a surface effect (to get some "smooth flow“?)

* For other reasons.