Not English/Old Dog:
Here is from a post several years ago describing the finish Wallace Gusler uses:
"I order it on-line: Senefelder's Liquid Asphaltum, manufactured by Graphic Chemical and Ink Co. 728 N. Yale Ave. PO Box 27, Villa Park, Illinois 60181.
Wallace showed me this technique decades ago and he has certain % mixtures, but for work i do , I've started with 1/5 asphaltum/raw linseed then test on various woods until i get the 1st coat tone i like (usually pretty heavy on the asphaltum- as i like the dark tone). Ive taken a cue from Wallace, he keeps his in an old glue pot, my concoction stays in an old damaged canton porcelain mug that i cover with a pine lid (i carved a recessed ring that fits over the mug rim) to keep it from gumming up too severely. when i want yo use it, i just warm it on an old hot plate out in the shop until smooth, then apply with fingers. Also, I have used non-polymer stains (e.g. water or alcohol based stain) as a color base, then apply oil/asphaltum method with really nice results.
Once you get the color you like, rub with boiled linseed oil to harden the finish, just remember, this procedure will prevent any additional penetration of new applications of asphaltum, that said however, the color will continue to darken a bit over the years."
***not sure I'd use this method for conservation of an antique as it's a bit difficult to control for blending color/patina etc.; but on contemporary projects its a pretty cool option***
Bruce
