HOW TO MAKE INTAGLIO PRECISIONMASKS

The Principle

• When PrecisionMask film is exposed to a small amount of light, only a thin layer hardens. Exposing a little more gives a slightly thicker layer. And so on until the full thickness of the film is achieved. The PrecisionMask Intaglio process takes advantage of this by exposing through a continuous tone film master (CTM) of the required image. In its darker areas, only a little light gets through this film positive and thus only a thin layer of the PrecisionMask film hardens. In the lighter areas, more light gets through thus giving a thicker layer. The clear areas give full thickness and the black areas leave holes like a normal stencil.

• So, when the PrecisionMask film is washed out, the resultant "stencil" has variable thicknesses, according to the various levels of continuous tone in the CTM. The PrecisionMask film is then processed and applied normally. When the Intaglio PrecisionMask is shotblasted, the various areas of the image wear away more, or less, quickly according to the thickness of the mask. Thus exposing the glass to the blasting process for different amounts of time. Thus cutting different depths in different areas of the image. After washing off the remains of the PrecisionMask, a very light polish with a cork wheel and pumice is used to bring out the highlights.

Preparing the Image

• In the example thistle image, the black veins on the leaves and stem give clear holes through the mask, whereas the lighter areas adjacent to these allow a fairly thick layer of PrecisionMask. Thus the veins start to engrave immediately, as do the darker outer edges of the leaves. The mask then wears away progressively from the outer leaf edges toward the centre as blasting proceeds, whilst the clear holes representing the veins are being blasted all of the time. Thus, when the last vestiges of the PrecisionMask are blasted away, a sharp step is left between the vein and the leaf immediately next to it. When polished, this gives the impression of a leaf with a darker centre, with a light vein running through the middle of it. Also, because intaglio cutting in glass gives rise to an optical illusion, the relatively deeper the cut, the relatively nearer that part of the image appears to the observer. Thus the vein gives the impression of standing proud of the leaf.

• The image is built up using a vector drawing program (such as Freehand) by using a series of greyscale blends, tones and graduated tones in the range 65 to 85%, plus 100% and 0% for the black and clear areas. These greyscales represent depths of cut, not visual tones (you cannot simply use a photograph - this illustration shows you the difference between a photograph and an intaglio artwork of the same image). The image is then imported into an image manipulation program (e.g. Photoshop) for final adjustment and for supply to the bureau.
• To build such an image, the artist needs to have an understanding of engraving principles and practice, together with a good working knowledge of the software, both of which are far beyond the scope of this basic overview. We can provide individual training, but a good standard of basic knowledge will be required for it to be of benefit.

Output, Exposure & Blasting

• Continuous tone output is only offered by a small number of high end bureaux (we use GBM Group plc of Manchester, UK). Ask for size for size, right reading, emulsion up, continuous tone positive transparency. Include an identical test step wedge (40, 60, 80 and 100% blocks) on each output. Ask the bureau to measure the densities of this wedge on your first output and, provided it works satisfactorily (good solid black and good clear clear areas), supply them with these density readings and ask them to match them whenever you order again. This will allow you to fine adjust your subsequent artwork and to achieve standardised results.
• The exposure settings require individual adjustment to achieve the correct balances of film thicknesses. As each exposure setup is unique, there are no set calibrations. Trial and error will be necessary!
• Use very fine, well worn grit. Stop engraving any given area of the image immediately all of the mask in that area has been blasted away. Any further blasting will only blur the image. After blasting, lightly polish the highlights as mentioned above.