Cabinet Cards for portraiture became popular in 1866. They are usually about 4.25" x 6.5" in size and are thicker than CDVs or Cartte de Visites, which are about 2.5" x 4".  Less common are "boudoir" cards, larger versions of cabinet cards, which are from 4.5"x 7.5" up to around twice the height of a standard cab card.

The earliest cabinet cards were backed by Bristol Board, the predecessor of press board or cardboard. Bristol Board was not layered in the way of press board and cardboard, so if there is evidence of layering (the "sandwiching" of multiple layers of paper) of the backing, the card is from the 1870's or later.

Cabinet Cards were originally used primarily for landscapes, being adapted for portraits in 1866. They quickly gained popularity during the 1870's and generally replaced the Carte de Visite in the 1880's. With the advent of the snapshot in the 1890's, their use began to decline, though they remained popular into the 1910's, with the last being produced around 1924.

Post 1900 Cab Cards had larger margins around the photos, often featuring elaborate embossed borders.
We can gather clues as to the date of a cabinet card from several factors, including the card stock, corner and edge style, stock colors, photographers ad or 'mark' and type styles. The other primary tool for dating cab cards are the fasions in the photos. Then as now, women's fashions in particular changed frequently and can often help determine the date to within a few years. There are a number of good resources on the web for this, and I won't delve into that aspect in this document. 

Here are a few clues to look for:

Card Stock

• 1866-1880 Square, lightweight mount
• 1880-1890 Square, heavy weight card stock
• 1890s Scalloped edges

Card Colors

• 1866-1880 Thin, light weight card stock in white, off white or light cream. White and light colors were used in later years, but generally on heavier card stock.
• 1880-1890 Different colors for face and back of mounts
• 1882-1888 Matte-finish front, with a creamy-yellow, glossy back.

Borders

• 1866-1880 Red or gold rules, single and double lines
• 1884-1885 Wide gold borders
• 1885-1892 Gold beveled edges
• 1889-1896 Rounded corner rule of single line
• 1890s on... Embossed borders and/or lettering

Lettering

• 1866-1879 Photographer name and address often printed small and neatly just below the image, and/or studio name printed small on back.
• 1880s on... Large, ornate text for photographer name and address, especially in cursive style. Studio name often takes up the entire back of the card.
• Late 1880s-90s Gold text on black card stock
• 1890s on... Embossed studio name or other embossed designs