Analog Prints Aren’t Analog Anymore
These days, we tend to think of printed collection objects as falling into either the analog or the digital, the old or the new. To most collection caretakers the analog objects feel familiar and predictable, while digital hardcopy seems to have an aura of mystery and suspicion, especially surrounding its ability to survive over time in the same ways as the older, more “reliable” materials. While we are all aware that a variety of new, innovative technologies for printing have become popular over the last few decades including inkjet and laser printing, not everyone is aware that what we have been referring to as the analog processes have been incrementally digitized over the same time period. It is now rare to have a totally analog-printed object. Analog and digital printing systems have slowly merged to improve the characteristics of each. Digital printing has borrowed from analog technologies as analog has reciprocally borrowed from digital. The modern laser printer is a digital version of the old photocopier. The rosette screen patterns from traditional lithographic offset printing are giving way to the randomized dot patterns of the digital offset plate. Color photographs, once printed through negatives, are now exposed by laser or light emitting diode. Below we will discover how each of these three common analog systems have become “digitalized”.
From the 1950’s to the 1980’s, all photocopiers created a copy of a document by reflecting light off the original onto a special pre-charged, photo-conducting drum. The object to be duplicated was placed face down on a glass platen where a light (the familiar green glow) was passed across its surface. The white areas of the document reflected high levels of light which neutralized the charge on the drum. The black text reflected little light, so the charge in those areas was retained. Next, an oppositely-charged toner was applied to the drum, which would stick to the remaining charged areas recreating the original text/image. The toner would then be transferred from the drum to paper and fused to create the final copy.
Because the toner was just black, and not various levels of grey, it could not adequately reproduce images which need subtle variations in tone. This worked great for text, but performed poorly for photos often resulting in misshapen blobs that only slightly resembled the original scene (see figure 1). Color photocopiers could create an approximation of the original object’s colors, but they too did a poor job recreating variations in tone between the extremes of light and dark.
The first digital photocopier became available in 1987. This device, which combines an electronic scanner and a laser printer in one unit, produces much higher quality reproductions than the old photocopiers. While the final output (toner on paper) is basically the same now as it was 50 years ago, the path to print has changed. The main difference is that the original is scanned first into a data file and then a laser is used to expose the charged drum. Light reflected directly from the original is no longer necessary. Because the scanner does a better job capturing the image of the original object being copied and the internal electronics of the laser printer can improve text and picture quality before output, prints from these devices are dramatically improved over those of the analog predecessor. By first converting the pictures to be duplicated into halftones, the blobbed-out look of the old photocopy is eliminated (figure 1). All photocopiers today are these combination scanner-printers (figure 2).
The most significant change to offset lithographic printing has been computer-controlled exposure of the printing plates. For much of their history, offset printing plates were created much like photographic prints from negatives. A half-tone image was created by exposing the original image through a screen onto special, high-contrast litho film to create a halftone pattern. The litho film was then used to expose the light sensitive printing plate. Typically the screens used during the 20th century created the half-tone patterns with the dots evenly spaced apart but varying in size. This was called amplitude modulated (AM) screening (figure 4). Dark image areas had large dots and light areas small dots, but the dots were all evenly spaced. The printing plate was then placed into the press and large numbers of impressions from the plate could be made. In color offset printing a separate plate for each ink color was required.
Now computers can create the printing plates directly (figure 3), eliminating many time consuming steps and allowing for more flexibility in how the image forming dots are organized. By direct exposure of the plate with a laser, the dot patterns can be manipulated to improve image quality. Frequency modulated (FM) screening produces small, fixed-sized dots that vary in direction and distance (figure 4). This can eliminate the obvious screen pattern often seen in earlier AM screened offset prints. As with photocopying the paper and ink remain the same even though the path to print has been digitized.
Traditional photographs were created using the silver-halide process which, on a microscopic level, is characterized by image forming grain. Silver-salts, embedded in a gelatin coating on a paper or plastic substrate, were light sensitive and captured the image forming light passed through the camera negative. During chemical processing the silver salts were converted to very small particles of metal silver to create a black-and-white image. In color photographs the metal silver was replaced with colored dyes to create the wide variety of hues and tones we see in our photos.
In the 1990’s, photo processing labs began scanning negatives and then using lasers or LED arrays to expose the photographic paper instead of exposing it right through the negative. This digital step allowed for better color and exposure control and thus image quality for customers. Special photo paper was developed for this process that matched the light quality of the lasers or LEDs. Sometimes the words “Digital Photo Paper” (or something similar) is printed on the back of these prints. While the new photographs are printed digitally, the paper itself is chemically and physically similar to the papers printed from negatives years ago. As such, they need no new special care practices. Under the microscope, you can sometimes see faint lines from the digital exposure; however, technological advances over the years have made it so the lines are much less apparent.
Permanence and Preservation
Luckily, because the papers and colorants are basically the same for both the analog and digital versions of these technologies, the care practices are also the same. Existing best practices should be followed.
Still, there are three important ways that the new materials vary from the old. First and foremost is that over the last few decades, while the digital printing technologies were being merged with the analog, the paper industry simultaneously moved from producing primarily acidic papers to mostly alkaline. For this reason the more recent papers can be somewhat more durable for long periods of time in collections. Secondly, various scientific developments to the printing colorants, including improvements to fade resistance and adhesion to paper, have also led to longer lasting prints.
Counter-acting those advancements, however, has been the “green” movement which has pushed manufacturers to include greater and greater concentrations of recycled content in paper products. In fact, in 1998 President Clinton sign Executive Order 13101 which requires all government printing to be on paper that includes at least 30% recycled content. The effects of the quantity and quality of recycled content on long-term stability of paper have yet to be fully understood. It seems logical that they will not have a beneficial effect, as mixed sources for the pulp can introduce a variety of potentially harmful ingredients into the new paper. Additionally, due to the repulping process, recycled papers contain shorter fibers than those made from virgin pulp making them physically weaker.
So in general, advances in printing, colorant, and paper technologies during the transition from analog to digital has resulted in potentially better-quality and longer-lasting prints. Of course there will always be materials produced as economically as possible with little concern for permanence. These ephemera will be created using the lowest quality of ingredients and will be more likely to rapidly degrade. If these are also to be ingested into collections, conservators and others must be on guard to spot them and make sure their individual needs are met.
More information on how to care for these materials can be found at: http://www.dp3project.org/preservation/storage-recommendations