Heliogravure VII – Observing the Lateral Etching

Cu_29_65_Gris_96Single or binocular loupes are often used to observe the effects of the etching on the surface of the copperplate. Depending on the kind of resin or screen used, it is sometimes difficult to view in detail what happens at this level. In some cases would be very useful to take a picture in order to compare or remind in the future. A fine device to do that is the ProScope MicroMobile from Bodelin Technologies (Fig., 1).

Fig., 1. ProScope MicroMobile with the Apple iPhone 6s attached on top. (Click on the image to view an enlarged version. Image taken from Bodelin Technologies https://proscopedigital.com/product/proscope-micro-mobile-iphone-6-plus/)

The ProScope MicroMobile basic unit incorporates a lens system from Edmund Scientific with a magnification power from 20x to 80x, an adjustable LED illumination system, a built in desktop stand and a battery container with USB charger connection. Over this basic unit it can be attached a plastic sleeve suited for the given cellular phone or tablet. This lens system acts as a photomacrography converter for the cellular phone or tablet camera lens. If we want to use more than one device, we need to buy only one basic unit and as many sleeves as devices. The Fig., 2 shows the device taking a picture from a test target copperplate in order to determine how the plate is affected by the lateral etching for a given etching sequence.

Fig., 2. The ProScope microMobile assembly taking a picture from a test target plate. In the cellular phone screen can be observed the magnified image of the etched screen (click on the image for an enlarged view).

On top of flat surfaces, the ProScope MicroMobile can be used as an enlarging loupe, sharing with other people the viewing experience. This is very interesting in teaching purposes. Through the device camera, both still pictures or videos can be taken. This last utility is very interesting because when the image is viewed in a computer screen, it is enlarged again depending on the relationship in size between the camera phone pixels and the computer screen pixels. As an example, the Fig., 3 shows a picture taken with an Apple iPhone 6s camera through the ProScope MicroMobile. Viewing the image in the screen of a MacBook Pro Retina 15” laptop, the total magnification is of about 100x. With a non Retina computer screen, the total magnification is even higher. Such a magnification is not available without specialized and expensive devices (See Fotomacrografía for a better detailed explanation. I’m sorry, in spanish).

Fig., 3. Magnification of an inked an wiped plate showing a little area corresponding to a black surface (click on the image for an enlarged view).

In order to perform measurements from the pictures taken with such a device, there is an app, the ProScope QC, allowing to display an overlay with a measurement scale on the device screen. The overlay can be also incorporated to the registered image. The reference scales shown in the Fig., 3 and 4 have been incorporated by digital image processing after a calibration procedure. The Fig., 3 was taken from a plate black region after inking and wiping was completed. The Fig., 4 is the result after applying a threshold to the image in the Fig., 3. This binarization allows to measure which is the ink coverage after etching (and lateral etching). In the case of the example, a plate black area coming from a digital screen with a 45% of black coverage, results in an etched plate where the inked area covers a 65% of the total surface.

Fig., 4. Thresholded version of the image shown in the Fig., 3 (click on the image for an enlarged version).

Then, electronic devices and digital image processing software can help us understanding and measuring some practical phenomena. In this case, we have quantified the effect of the lateral etching for a given situation.

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