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Looking at old and new prints with an USB microscope is revealing and with some experience can lead to their identification. Printmaking history is fascinating as well as a complex subject. I like to share in this post some basic hints on their identification using the USB microscope but heartily recommending further readings [1, 2], since the number of techniques and variations is extraordinary, so a definitive attribution deserve an advanced knowledge. Though, even if the subject is complex, this doesn’t mean we cannot have some good time, experimenting a bit with prints. A great online resource is the IPI (Image Permanence Institute) Graphics Atlas .
Pigments Checker is for photographers, conservators and scientists interested in technical documentation of paintingss. It has 54 swatches of historical pigments designed for infrared photography, ultraviolet photography and other technical photographic methods for art examination. Check it out!
Pigments Checker is a collection of 54 swatches of historical pigments that have been applied using gum arabic as a binder on a cellulose and cotton watercolor paper, acids and lignin free. This paper is not treated with optical brighteners, it’s slightly UV fluorescent, and it reflects IR. Two cross-hair lines, 0,2 mm (vertical) and 0.4 mm (horizontal) are printed on each swatch of paper before the application of paint, in order to have a means to evaluate the pigments’ transparency in the IR and IRR imaging. Among all the pigments and their varieties ever used in art these pigments collection select the most used ones from antiquity to early 1950’.
Pre-photographic printing methods are classified in three main categories: Relief, Intaglio and Planographic. This post covers the first two.
This is the oldest of the printing techniques. On the relief block – wood or metal – the non-printing areas are cut away and the ink is applied to the remaining raised areas by dabbing or with a roller. Then the ink is transferred by laying a sheet of paper and applying pressure.
Relief is identified by:
- Edges’s rim. The process of transferring the ink from the block applying pressure produces a characteristic rim on the edges of the printed lines. This is a sign characterizing only relief printing.
- Embossing. Relief printing can show embossing on the back of the paper caused by the pressure applied. RTI (Reflectance Transformation Imaging) is the most suited photographic method to document embossing).
Intaglio means incising in Italian and this technique was developed in the 1500s. On the contrary to relief, the ink is held in grooves on the block’s surface.
Intaglio is identified by:
- Varying ink intensity. The main characteristic of this technique is to show lines with varying ink intensity while in relief the intensity of the ink is always the same. Since the grooves’ depth can be adjusted, the ink collected in it would vary and this translates in darker or paler printed lines.
- Raised ink. In strong dark lines the ink considerably rises up from the paper.
Intaglio by Engraving
There are two techniques to cut the lines of an intaglio print, engraving and etching. Engraving is the oldest method and it uses a burin with sharp V-shaped cutting section, which is pressed gradually down onto the surface of a copper plate and then driven more or less deeply through the metal. It will be raised up at the end of the line to lift out a sliver of copper.
Intaglio by engraving is identified by:
- Shape of the line. It has clean edges, tends to be pointed at each end and to swell or diminish during its length. The controlled act of engraving also gives the line a formal character.
Intaglio by Etching
In the etching techniques the cutting is done by an acid and the artist can draw freely on the wax covered copper plate.
Intaglio by etching) is identified by:
- Shape of the line. Etching uses a rounded needle that passing through the wax ground give a more blunt end to the line than the engraving tool. And the very slight crumbling of the wax to either side of the line, combined with the somewhat uneven action of the acid, results in the less precise edge to the line than in an engraving. Etched line will be of the same width along their length, while the burin gives swelling shapes.
References B. Gascoigne “How to identify prints” Thames and Hudson, 2011.  A. Griffiths “Prints and Printmaking” British Museum Press; 2nd Revised edition, 1996  http://www.graphicsatlas.org/