Adding Asphalt to Colophony Varnish

[Shunyata]

Is this even a good idea?

How much, and at what point in the process?

Any suggestions for how to test  impact without committing a large batch of varnish?
 

Does this add significant coloration, or just alter tint?

 

[Don Noon]

It is useful for depressing (or saddening, dimming, darkening) a color that's to pure and bright, as long as it's done in moderation.

As for the other questions, I made up a 1:1 Gilsonite (asphaltum) varnish, which is extrmely dark and useless on its own.  Then I use a small amount of that to adjust the main varnish color.  The amount is determined by what looks good, and you can make any size batch you want.

[Mike_Danielson]

This question comes once in a while because you do not do your homework.  There is a lot of information on varnish and pigments in the literature, particularly on how they age, if you want to look.  Let me give you the quick answer--never add this stuff to varnish.

[JacksonMaberry]

12 hours ago, Don Noon said:

saddening

Paging @Nick Allen, in case he needs a quick chuckle.

[Nick Allen]

On 9/24/2023 at 2:27 AM, JacksonMaberry said:

Paging @Nick Allen, in case he needs a quick chuckle.

lol

[Dr. Mark]

On 9/23/2023 at 5:32 PM, Mike_Danielson said:

There is a lot of information on varnish and pigments in the literature, particularly on how they age, if you want to look

I'll byte - oops 'bite'...hmmm mummy brown....not really...mummies used as locomotive fuel - no...wrappings used by the paper industry - no.  Mummies everywhere...Ah!  Here we go: 

"Asphalt is a pitch-like substance that remains after the evaporation of the volatile elements of petroleum that has come to the surface. There are, for example, several places in the world where there are asphalt lakes. The largest lake is located on Trinidad, and is still a source of natural bitumen. In the Middle East asphalt used to be extracted mainly from the Red Sea, where it had ended up in solidified form after seeping through fissures and hot springs. Alongside ground up mummies, this natural asphalt was also used for the preparation of oil paint. Linseed oil would be heated, after which asphalt was dissolved in this. Asphalt should therefore be regarded as a dye (pigments applied in oil paint may not dissolve in the oil), with all its negative properties. Dyes have a tendency to bleed; the colour penetrates other paint layers or spreads inadvertently to the surrounding area, also when the paint layers are dry. But asphalt does much more! It causes the paint film to wrinkle and contract until there is little left. What’s more, asphalt prevents the paint from drying throughout, which can then sag as a consequence when temperatures increase. In short, a disaster for every oil painting."   https://tinyurl.com/4nncaz5b

However, it's never advisable to stop with a single source (esp. an internet source).  Here's something from a Natural Pigments website (https://www.naturalpigments.com/artist-materials/asphaltum-bitumen) : "Although asphaltum has a bad reputation in art history for ruining works of art, there are examples of its use where this is not the case [One may ask for the evidence that successful applications were actually asphaltum as we know and love it...]. It may not be so terrible in oil painting, especially with the second preparation method. Natural Pigments will offer Asphaltum as part of Rublev Colours Artist Oils.

Although many aspersions have been cast upon the use of any asphaltum in oil painting, it is interesting to note these comments by Church:

‘The disadvantages attending to the use of these coal-tar browns and of ordinary asphalt are two-fold. Not only are they treacherous on account of their easy fusibility, but they are liable to stain contiguous pigments by reason of their solubility in oil or varnish. When used successfully by the older artists they were always introduced sparingly, or were largely commingled with more solid paints.’ (1901, op. 236)

Church had distinguished between the source of asphaltum earlier in his 1890 edition by endorsing the use of native asphaltum when properly prepared:

‘The operation of roasting native asphalt—keeping it over a slow fire ‘till it will boil no more and becomes nearly a cinder’—was recommended by Williams in his “Essay on the Mechanic of Oil-Colours” (1787), and furnishes a perfectly satisfactory and safe product.’ (1890, p. 208)

Personally, I think asphaltum in oil painting should be revisited, but in carefully controlled and limited circumstances, to determine if it can be employed safely used in modern artworks.": 

"It was at one time believed that bitumen was used in the bandages of mummies, but this was generally not the case (instead, balsams were used). Perhaps this error resulted in some confusion, which may have lead individuals to grind actual mummies for use as a pigment, perhaps as an alternative to asphaltum. Of course, the origin of the English word “mummy” is from the Persian or Arabic word “mumia” or “mumiya,” meaning asphaltum or bitumen, which may have caused some confusion about the real source of this pigment."   Go figure.