Duotone options are a superb way of making higher quality monochrome pictures as they use more than one ink for the image. Printing with a single black ink is often far less satisfactory.
There is also the slight advantage that Duotones produce smaller file sizes than toning with an 'RGB' image file.

Duotones are available via Image > Mode > Duotones (from a 'Grayscale' starting point).

NB To create a Duotone we need to begin with a Grayscale image. This could be an image originally scanned as 'Grayscale' or one that's been converted to Grayscale via, Image > Mode > Grayscale (if the image includes 'layers' you'll be given an option to 'flatten' the image). Then, go to Image > Mode > Duotone.

The next task is to 'load' the duotones and once there, two possibilities presented. We can open a range of pre-set duotones or create our own from scratch. Perhaps the easier method to begin with is by the pre-set route. As you will discover, these 'pre-set' tones may be altered to ones own requirements - more of which later.

Photoshop V5

Image > Mode > Duotone. This will probably result in a 'Monotone' box appearing upon the screen. No matter what Duotone box is presented, you'll need to load the type you require and this is the route you must follow.

Click 'Load', then in a mini version of the familiar 'Windows Explorer' structure, go to your Adobe folder.
Next, choose Photoshop > Goodies > Duotone Presets
Next, go to 'All Versions (below)

Image > Mode > Duotone. This will probably result in a 'Monotone' box appearing upon the screen. No matter what Duotone box is presented, you'll need to load the type you require and this is the route you must follow.

Click 'Load', then in a mini version of the familiar 'Windows Explorer' structure, go to your Adobe folder.
Next, choose Photoshop > Adobe Photoshop Only >Goodies > Duotone Presets
Next, go to 'All Versions (below)

The 'Duotone Options' dialogue box appears

Next, select either Duotones, Tritones or Quadtones. Each of these presents yet more options so let's take a look at each one.

Duotone, this will use two inks for the image

Tritone, this will use three inks for the picture

Quadtone, this will use four inks for the picture

Each of the above types of 'Duotone' will give access to many pre-set tones, plus what at first appears to be a bewildering number of ways to make your own tones.

We'll begin with the pre-sets as they give an instant starting point.