Below is an overview explanation of the terms we use to describe our prints.
There are three basic types of mechanical prints - below are over simplified definitions;
Relief - A plate is carved and inked and the ink from the top surface is transferred to the paper (think woodblock). Intaglio - A plate is carved and inked in the recesses. The ink from the top surface is wiped off and the ink in the recesses is transferred to the paper (think engraving). Planographic - Operates on the principle that water and oil don't mix. basically a plate is covered with grease where no ink is desired (ink does not adhere to the grease). The ink from the uncovered surface is transferred to the paper (think lithograph).
In addition, there are related processes that while not prints in the strictest sense of the word, are often lumped in. A few examples are; Screen-prints, Stencils (Pochoir), and Process photography (silver Gelatin etc...) - these are outside the scope of this page
A special note about gravures since that is our main focus. There are a variety of methods that fall under this name two of which are used to reproduce "art" photography. We deal with mostly sheet-fed (aka "screen") gravures, and on a rare occasion we may have a hand-pulled photogravures. The nomenclature "photogravure" is commonly used for both types (which leads to a lot of confusion), so we always use our adjectives when we describe a hand-pulled item. If there is no printing description in a listing then the item is a sheet-fed gravure. both of these methods start with a negative that is exposed onto a specially coated copper plate. The light interacts with the coating, etching the copper underneath - the more light, the deeper the etching. The plate is then used to print (or engrave) the image with ink.
As far as gravures, I compare them to Lithograph's in the painting world, not by process, but as a similar level of product. Hand pulled gravures are similar to limited edition, hand made lithographs. Sheet-fed gravures are similar to commercially published lithos (such as those in "derriere le miroir" or "C'ahiers D'art"). Price is quite often a function of rarity and desirability.
hand-pulled (dust grain) photogravure (Intaglio) -Grain gravure isa fully manual process usually utilizing the highest grade papers and inks that produces stunning prints. Some consider these reproductions superior to the silver gelatin prints because of the permanence. The tone defining grain is organic rather than a screen. The ink is thick and rubbed deep into the plate by hand. The plate is run through the press slowly, one sheet at a time, to insure the complete transfer of the pockets of ink deep into the oftentimes handmade tissue or paper. These are identifiable under magnification by the randomness of the grain and the silver/white specks ingrained - these can run into the hundreds of thousands of dollars, especially the early Steichen and Stieglitz prints, but are generally in the low thousands
sheet-fed (screen) photo gravure (Intaglio) - A commercial process utilizing sheet-fed presses where individual sheets of paper are fed into the press. Rather than using an aquatint grain to break up the image in order to print intermediate tones, a cross line screen is used. In addition the paper used is usually commercial grade, and the inks diluted somewhat to help speed the process. These are identifiable under magnification by the square grid, honeycombed pattern formed by the ink. Tonality is achieved by varying the shade of ink in the squares. These generally still provide much better tonality than halftone printing. Many of these are also rare and the general price ranges from mid tens to low thousands for limited edition plates. Once again, rarity, quality, and desirability dictate the price
collotype (Planographic) - A photomechanical printing process that gives accurate reproduction because no halftone screen is employed to break the images into dots. In the process, a plate (aluminum, glass, cellophane, etc.) is coated with a light-sensitive gelatin solution and exposed to light through a photographic negative. The gelatin is hardened in exposed areas and is then soaked in glycerin, which is absorbed most in the non-hardened areas. When exposed to high humidity, these areas absorb moisture and repel the greasy ink. The hardened areas accept the ink, and the plate can be used to print a few thousand copies of the positive image. Collotype prints can be readily identified by the presence of image reticulation, a product of the finely cracked gelatin plate used to print the image. This can be seen using low magnification, such as a loupe. Because of the short life of the coated glass plate (a few thousand images), Collotypes are inherently limited editions and generally run low hundreds of dollars to low thousands
duotone - Duotones are the result of printing a grayscale image in two different ink colors. Printing photographs by the duotone method produces a richer, longer tone scale than is possible using only one color. Duotones have been in existence since the early days of photography: most consumers are familiar with sepia toned prints, for example, which use various shades of brown. Both gravures and halftones can be utilized in producing duotones.
photo-engraving aka relief or letterpress halftone (Relief) - Tonality in both halftone processes is achieved via spacing (density) and size of the ink dots, but the dots are all the same shade (color). Under magnification both of the halftone methods appear as a series of dots much like a Lichtenstein or comic print. Relief halftones tend to have the ink gravitate to the edge of the dot making the center seem a little lighter
offset halftone (Planographic) - The modern variation of the half-tone belongs to the planographic group, and has been called offset lithography, photolithography, or photo-litho process. It works on the principle of lithography, where there is no relief on the printing plate, just areas that attract or repel water and greasy ink. The dots in offset halftone are the same color throughout without a lighter center
mouse over the images below for an explanation of each photo (from www.graphicsatlas.org - visit them for more info)