Asphaltum

Asphaltum is an oil color that was used darken paintings, and to mimic the look of what happened to varnish when it aged. As it came from tar, it produced very poor results over the long term; and as the pigment was unstable, it destroyed paintings with cracking. Modern equivalents are of a similar color with similar impact, but without the chemical drawbacks of the older formulas. You might find asphaltum useful if you wish to created an aged effect for your painting, or if you want to recreate a smoky haze or similar glaze.