Duotones, tritones, and quadtones use spot color inks and multiple passes on a printer. They are expensive to produce because of the separate plates and press washes.
Photoshop has a duotone mode. Printing these images on an inkjet printer results in a pseudo-duotone. These can be very lovely images and nearly indistinguishable from a true duo/tri/quadtone.
If all you want to do is produce a toned B&W print, there is no need to convert your image to Duotone mode. You can stay in 16-bits per channel and RGB/CMYK/L*a*b with the TLR B&W Toning action set.
You can use the TLR B&W Toning action set to apply a variety of tones to your monochrome images. Just be sure you have a color image in RGB, CMYK, or L*a*b. The actions apply a gradient map to your image rather than converting to Duotone mode. It is not even necessary to convert your image to monochrome first, although this action set is the perfect complement to my TLR B&W Conversion action set.
Digital B&W fine art prints will especially benefit from the choices in this action set, especially if you use something like an Epson 2000P, 2200, 5500, 7500, or 9500 printer.
The "Gray Neutral" setting is designed to produce neutral B&W images. Other variants include cooler and warmer grays and also grays with a green or mauve cast. Some digital B&W photographers strive for a look that resembles selenium tone prints. The "Selenium" action produces prints that have the look of selenium tone prints. Platinum tone prints are another favorite. The "Platinum" action simulates platinum tone prints.
Available tones include:
Blue
Brown
Burgundy
Cyan
Green
Magenta
Mauve
Orange
Purple
Red
Yellow
Sepia Tone 1
Sepia Tone 2
Sepia Tone 3
Gray Green
Gray Mauve
Cooler Gray
Neutral Gray
Warmer Gray
Platinum
Selenium
With the TLR B&W Toning action set, you get adjustment layers that can easily modified. You have complete control over the resulting tone by adjusting the gradient map.
http://www.thelightsrightstudio.com/TLRB&WToning.htm
Enjoy!
Cheers,
Mitch