I have purchased ultramarine blue in the past and it began to smell. I was wondering what I should add to it to remedy this situation. Currently, this pigment sits in water and I have added some alcohol (70% isopropyl). But I wasn’t sure how much to add. I am planning to mix it into egg tempera but I don’t want to spoil the capabilities of the egg yolk. So I am letting some of the water/alcohol mixture evaporate before I actually use it. Any tips?
Hello there,
For it to start smelling is peculiar, so I hope you bought it from a reliable supplier. Its normal dusts are not that strong smelling so it’s likely moisture mould that started to grow.
Ethanol to a sterilising level needs to reach 70% in total. So if you’ve just mixed some 70% propanol to water, I can’t guarantee it disinfected anything.
However what you can do far more simply:
First wash it all back in water, then boil the water with the pigment generously, finally sieve and dry. Under sunlight is a plus and driest air you can have.
Basically just boil-sterilize your water and then dry all the pigment back, and store it dry. Any still water or moisture will eventually grow something over time.
Good luck,
Lussh
Kremer’s ultramarine dry pigment selections show different levels of free sulfur. It is therefore foreseeable that some producers of ultramarine leave more sulfur residue in their pigment for sale than others. I don’t know how Kremer’s selections compare but I can imagine that there are lower-tier suppliers that leave more free sulfur in.
Free sulfur in ultramarine as well as in cadmium and vermilion might cause a reaction with some pigments like lead “carbonate” white (in quotes because it’s two molecules).
— SRS
Hi,
I only know what little I have read about the pigment. The ultramarine sickness, from one conservation article I recall reading, was about some inherent instability in the molecule — not directly related to free sulfur impurity in the pigment mix. The instability causes, over the very long term, the destabilization of the molecule which results in the loss of color saturation (a grey color). I think light exposure (radiation) accelerates the process but am not certain. I recall the article saying that finer grinds may be more susceptible. I don’t know if free sulfur exacerbates the issue and/or some other additive, like aluminum ions. I wish I could be more helpful but I am both an amateur and haven’t the best memory.
What I came away with from the article was that if someone wants their painting to stay bright blue for hundreds of years, a pigment other than ultramarine is probably a better choice, such as (perhaps) PB 28 and PB 74 — both of which are cobalt blues. I think those can have issues due to pH (possibly acidity), too, though.
— SRS
Many pigments, when hydrated in paste form, emit a slight odor. I currently have 20 open jars of pigment pastes (natural and synthesized colors, ultramarine among them) in my studio (I’m letting them dry out so they become “pigment cakes”, or dry chunks of colors; this minimizes the issue of pigment dust) and the room smells faintly swampy. There’s always a bit of smell when I make pigment cakes and I’ve never had a problem with my colors.
The modern process of synthesizing ultramarine blue involves sulphur (it is, as a chemist told me, “a sodium-silicate zeolite trapping polysulfurs in a silicate cage”). Hence ultramarine blues can smell like sulphur (a rotten egg). The strength of the odor depends on pH: In a pH 6.5 or greater environment, ultramarine is stable. If its environment falls below pH 6 (becomes acidic), the color can begin to breakdown and release sulphur fumes. So if what you’re smelling is a strong sulphur odor, it might be a good idea to toss out the color.
Naturally occurring, genuine lapis lazuli has the exact same chemical formulation as synthesized ultramarine blue. There is a history of genuine lapis fading or turning dark, called “ultramarine sickness”, generally caused by acidic pollutants. The same thing can happen to synthesized ultramarine (since it’s chemically identical to lapis) – and yet, I’ve never personally heard of an artist experiencing problems with modern ultramarine blue, even among the many icon painters I know who preserve pigment pastes and egg yolk medium with vinegar (quite an acidic preservative). I’m not saying this means modern, synthesized ultramarine isn’t affected by acids; I mean to say only that the circumstances under which it happens must be unusual, or else I think we’d be hearing about more problems with modern ultramarine blue.
If mold is the culprit and the pigment has been smelly for a while, you’d likely see mold (white, green, there are different kinds) on the surface of the pigment. If it is mold, phenol is often suggested as a more effective anti-microbial than alcohol. Phenol is acidic (carbolic acid) but I haven’t heard of any issues with adding it to ultramarine blue. Again, the degree to which ultramarine is reactive to acids isn’t clear to me – it’s generally considered a stable color, I believe it takes a strong acidic issue to cause it to break down. So if there is a strong rotten egg smell, something in your studio environemnt my be affecting the color negatively. Or, maybe it is just mold. Good luck!
Hi SRS,
This is a topic I remain confused about. I understand that lapis lazuli and synthesized ultramarine are chemically reactive to acids and can darken in their presence, and that examples of Renaissance paintings that have this probelm are often cited. Yet, despite being in communication with many professional & student painters, and reading/posting on various painting sites (including MITRA), I’ve never heard of a painter – even those adding vinegar to lapis or synthetic ultramarine – that’s experienced a problem. Am I just not hearing enough antecdotal evidence, or are the circumstances under which this happens very rare (and, consequently, perhaps a moot concern)? I warn students about ultramarine blue and acids, but without more specific examples to cite, I’m not quite sure what I’m telling them! Thanks for your input.
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