Asphaltum, Bitumen or Whatever

[Kenneth Freed]

Quote from FE Church

"Kenneth, I believe you're right about it being asphaltum. I've only had asphaltum for a few months, but I've made good use of it. According to a post by George, Asphaltum is pigment melted into turps; Bitumen is pigment ground in oil. Asphaltum in mass is black; yellow brown when very thin; orange brown in middle thickness. Pretty much the color of Pepsi. I have not used Bitumen, but I did mix up a very small batch to study. Like Asphaltum it is black in mass. When thinned it becomes a slightly warm grey, with a barely discernable undertone similar to Asphaltum's thinned tone. I imagine figure painters (Bouguereau) would have had more use for Bitumen than Asphaltum. Asphaltum with no varnish mixed in dries rapidly (like 10-20 minutes thin and forms a skin in that time when thick) and is sticky and goopey. It will not hold impasto as placed and tends to puddle on the palette. I used cheap hardware store turps to make mine, so this might explain why mine is still soluable in turps after drying (it might also have to do with the fact that I let the sun heat it and not properly cook it), or maybe that's just a universal quality. Asphaltum that dried in mass is very brittle and looks like obsidion. The supposed problem is that Asphaltum hardens, but never truly dries. With Copal, it is more resistant to turps, it doesn't puddle as much, but still can't be used for impasto. Also, it takes some effort to mix copal with Asphaltum-it clotts before mixing fully. I recently tried Groves' Fir varnish- it mixed easily into the Asphaltum and gave it a "smooth" feel with mo stickiness or clotts. It did not puddle and it held perfect impasto. Also, when dry, it did not shatter when I pressed a fimgernail into an impasted area. It was still weak to turps scrubbing, like Copal, but didn't re-melt when gone over lightly with turps. I was also able to overpaint with normal oils with no cracking when applied fat or lean (Asphaltum is essentially a spirit varnish).

The fact that Rubens' works are 'alive and well' proves that Asphaltum in the underpainting can be stable. I imagine Rubens added something to make it easier to brush and harden enough so as not to remain soft while overpaint enbrittles over time. I don't think he used the wax and Copal combo, which was primarily an 1800s practice.

As for the color looking too warm, remember that Asphaltum is very transparent. I once underpainted a rock with white, yellow ochre, and Ercolano Red. When I glazed over with Asphaltum, the white area had the orange brown tone; the red had imtensified, almost like I glazed over with Madder; the yellow became an intense orange. If Rubens glazed Asphaltum over an earth color imprimatura, it would have taken on the earth colors' warmth. I, too, have never seen an Umber that looks exactly like that. Also, I have never seen an Umber that is totally black when applied thickly.

And if Rubens found a way to control Asphaltum, who's to say he didn't mix it with a warmer color. Frederic Church's sketches, which appear to have paints doused in Copal, often have a rich brown green color for grass and leaves. I think Church mixed Asphaltum with green. Another sketch has a rich brown grading into a red brown.

I'm not sure if they had it in Rubens' time (I'm pretty sure they did), but they didn't in Church's: the Legendary Syrian Asphaltum. For all we know, it was warmer than Gilsonite and other Asphaltums.

In page 17 of the old Underpainting and Layering Theory and Practice topic in the Oil Forum, there is a sketch(?) by Rubens with a yellow brown line drawing with black impasted areas occasionally. It looks exactly like Asphaltum to me. Furthermore, there's a section of the beast's foot where the fur has the effect of being glazed over the former lines. I imagine he did the entire thing at once, so only a color that sets fast, like Asphaltum, could achieve that effect (unless he used a varnish that caused fast set for all colors).

As for the books, I've always wondered whether these conservators actually used lab tests to determine colors or just looked at the pictures and guessed according to historical knowledge (I've seen them do both- I mean, we don't want to hear 'bright red,' we want them to tell us the artist used 'Vermilion'). If they did use tests, Asphaltum being a spirit varnish may not have been identified among the pigments."







Continuing our discussion of asphaltum, bitumen or whatever. I received my Gilsonite the other day and as predicted, I had it all over everywhere do to my less than careful opening of the bag. Very light weight stuff. I was initially interested in a few different combinations. I made a paint out of the Gilsonite by adding Natural Pigments Venetian Medium which since it contained glass would aid in giving body to the Gilsonite, drying capabilities, and sheen. It made a very rich paint with nice body. I then made a paint utilizing 1/2 Venetian Medium and 1/2 Groves Fir Wax. This made an exceptionally buttery and nice paint from a viscosity point of view. It could be controlled and applied with a hogs bristle brush and many of the translucent and textural qualities that I see in Rubens work up above could be duplicated. However it was impossible to thin out using a solvent. It did not react well to the precise kind of controlled painting that I see in the Rubens asphaltum appearing areas. I also tried Oleogel with the Gilsonite but it was also not controllable to the extent that I wanted it.

I think FE Church may have hit on the solution after experiencing first hand the problem of using Gilsonite and making it a paint. I think that it is likely that Rubens used a combination of pigments for this all pervasive rich brown that appears in his painting as well as in Andrea De Sarto and Vasari's underpaintings which remain unfinished. The working properties of Gilsonite as a single pigment do not appear to me to offer what is seen in so many Rubens underpaintings. However, the saturation, translucency, sheen and clumping of strokes and general visual qualities lead me to believe that some kind of Gilsonite, bitumen or asphaltum is part of the pigment combination. My next investigation is to take other possible suspects in the pigment world and combine them with the Gilsonite to see if I can more exactly replicate the qualities of this Rubens paint.

[Darren]

It is too bad that the old thread degenerated into etching, camera obscura and other issues but I am glad that you’ve resurrected it Kenneth, and with some experiential evidence no less!

As that old thread was drifting off I noticed some conclusions being drawn based solely on visual evidence. The current condition of Rubens’ paintings taken as evidence of the stability Asphaltum in an underpainting as well as the idea that his imprimature (plural) and sketch layers were composed of the same paint mixes are the two that stuck out for me. While visual evidence is certainly something to consider one must bear in mind the many factors that affect what we now see in the paintings themselves. Varnish discoloration, paint composition, paint color changes, original layer interaction as well as that interaction, both visual and physical, over time all color our current perceptions.

Until it is proven via contemporary writing and/or scientific examination no one can say with absolute certainty that Asphaltum was used by Rubens in either his imprimature or sketch layers. Experiential evidence however can prove or disprove that it is and was possible. With that in mind I look forward to reading and seeing more of your experiments.

Based upon the difficulty you’ve experienced when trying to thin out Asphaltum, as well as FE Church and Groves comments perhaps Asphaltum is more suited for sketching rather than wash-like applications? Then again, I believe that we do have written evidence of it being used in final glazes. If we’re after an imprimatura, the issue seems to be what to thin it down with. In a nearby thread George was discussing ‘fat over lean’ and how the principle is not as black and white as it seems. Perhaps thinning it with an oil/resin solution would not present fat over lean problems later on?

[Kenneth Freed]

Some trials this morning were intriguing to me. I used many different combinations of pigments (mostly available to Rubens), in paint combinations with Gilsonite. The one which I liked best, I have included here. The Gilsonite was ground in 1/2 heat bodied oil high viscosity, 1/2 pale grinding oil. This in turn was mixed with 2 parts Gilsonite, 1 part NP spanish earth, 1 part NP burnt sienna, 1 part bone black.

It seemed to represent best the textures of this rich brown paint in Rubens work. My belief at present was that Gilsonite is not suitable alone for the range of textures characteristic of Rubens work. The paint seemed to handle very well and set with all the brush distinctions well shown. How this paint dries, cures, and the longevity as well as the rewetting with solvent remains to be seen.

I will show the results on a small panel, keep in mind that most of Rubens rich brown paint was either over a burnt sienna and or a raw sienna imprimatura so the temperature of the paint will appear different over underlying paint.

[fechurch]

Kenneth, I would suggest you also try melting 1 part Gilsonite in 3-4 parts turps in a small container. This is the type my past post most refers to and the most transparent in my experience with the color. With this version, the Fir Wax alone does provide body and it can be thinned with turps (if it "hardened" on the palette, it may need to be scrubbed). There are three problems with this type, though.

1. It dries too quickly when exposed to air. After dissolving in turps, I would add a little oil, contrary to Groves' suggestion.

2. With enough turps, it always seems to re-liquify. It is a worry to me that when I keep having to swirl a turps soaked brush into my palette asphaltum that it weakens. As I said before, this may be because I didn't properly heat mine into the turps.


3. When making this version of asphaltum, there is an insoluable part that needs to be filtered out. It resembles tar in its gooeyness and black-blue color. I "cooked" mine in the sun, so maybe that's why this part came out so fast. I also stirred mine occasionally with a toothpick. When it was time to tube, the bad part had settled on the bottom of the container and I could just pour the good part in. By the end of the week, the bad part exposed to air thoroughly dried rock hard and could not be removed from its container. I recall one source (a book transcript online) saying you could make this part usable with much effort. That source also recommended filtering the Asphaltum with the pigment in a cloth bag suspended in the turps mixture.

Good luck, Kenneth, in your effort. I've found that there are better color results when only a little of other colors are mixed with asphaltum, as that preserves asphaltum's range of tones dependant upon thickness. For that source I mentioned, type in "asphaltum" and there should (on the first Google page) be a site with a treasure chest in the upper left corner. The imformation is somewhere on that site.

[Kenneth Freed]

Good suggestions thanks fechurch

[George O'Hanlon]

Originally posted by fechurch:
I recall one source (a book transcript online) saying you could make this part usable with much effort. That source also recommended filtering the Asphaltum with the pigment in a cloth bag suspended in the turps mixture.

For that source I mentioned, type in "asphaltum" and there should (on the first Google page) be a site with a treasure chest in the upper left corner. The imformation is somewhere on that site.

I believe the sources fechurch referred to are:

Arthur H. Church, The Chemistry of Paints and Painting,

Charles L. Uebele, Paint Making And Color Grinding

I have reproduced the information from Charles Uebele's book below:

Asphaltum Paints And Asphaltum Compositions
So called black asphaltum paints are often simply benzine asphaltum varnishes with or without admixture with coal tar. While the name asphaltum paint has become a synonym for something very cheap in the line of black paint, it need not deter the paint maker from placing a good article on the market. A good elastic black paint can be made by mixing 10 pounds grinders' lampblack in oil with 2 gallons raw linseed oil and 1/4 gallon liquid dryer, with 11 1/2 gallons benzine asphaltum varnish, thus producing 15 gallons black paint, that will stand exposure to the weather very well. An asphaltum composition, that is insulating and capable of resisting high degrees of temperatures is made by melting in an iron kettle 200 pounds gilsonite asphaltum with 40 pounds candle tar, and adding 30 gallons 160° coal tar benzol or solvent coal tar naphtha and 50 gallons 62° benzine for a 100 gallon batch.

[fechurch]

Thank you, George, for linking to that site. I remember those two sources, but the one I referenced was something else. I tried to find it, but couldn't. It spoke of preparing asphaltum in mass in a large container. I remember it also saying something along the lines of "only turpentine that evaporates without leaving a residue on porcelain should be used." I'm pretty sure it's on that site. If and when I find it, I'll post a link.

[fechurch]

Found it! Norman W. Henley and others' Henley's Twentieth Century Formulas Recipes Processes.

I think the one that tells how to make the insoluable part usable was another source. I have no idea where that one was.

[Darren]

The Uebele book seems to be about non-artist uses of paint. It does make me think of a question though. I wonder if inventories are available from 17th century color merchants? In other words, just like they had panel makers back then perhaps someone was in the business of making Asphaltum on a more commercial scale.

[George O'Hanlon]

Charles Uebele wrote a manual for paint manufacturers -- artists, house and industrial paints. It is an interesting read and a very accurate portrait of paint making at the beginning of the 20th century. e have found this book indispensable to crafting paints before the advent of additives.

We also have manuscripts containing recipes from the 16th and 17th centuries describing asphaltum and bitumen. These can be found in the books by Charles Eastlake and Mrs. Merrifield.