Here is the method I used to to establish the base-coat color for the mahogany woodgrain for my garnish trim. I used an original coupe door molding which had a 'good' sample of the original red/brown base-coat hiding underneath the backside of the molding where it had been 'protected' all these years.
The photo below shows the original base coat on the back side of the molding compared against the modern paint color swatch.
To achieve this match, I took the door molding to my PPG jobber and had them match this base color. They took their color prophet colorimeter and scanned the back side of the original molding. The computer analyzed it and declared it to be the same as Suzuki Red, OEM color code Z26. (PPG DBU formulation number 75083). The color as-mixed was extremely close and required no further tinting, as shown above.
The mahogany pattern is then applied on top of the cured base coat using Russet Brown rubber printers ink. Do not use black ink! It is too dark!
Trimmed stiff brushes and crumpled newspapers can used to apply the ink in a woodgrain pattern. Original grains were applied using rubber rollers and ink transfer from etched metal graining plates.
The ink is slow drying and can be wiped off if you want to try again and reapply it.
When it looks the way you want it, stop and let it dry for several days. After the ink is dry, the part can be top-coated with a urethane satin clear coat.
Above is an original coupe window molding which shows some of the original woodgrain pattern on the show side.
Pictured below are a series of photos courtesy of Tom Moniz which show the woodgrain pattern on a beautifully preserved original 1930-31 dash panel. Note the brown ink color. Thanks to Tom for allowing his pics to be added to Ford Garage!
Most original wood grained parts were produced using an ink transfer process using gum rollers on etched metal graining plates, and followed by minor brush touch-up by hand.