Cross Pollination of the Conservation & Digitization Team
Every item in a Cultural Heritage collection is unique and demands particular handling. Consider a collection of fragile bound volumes from medieval France that may have significant variation in binding fidelity, and require individual assessment and handling to prevent damage to those bindings. Nonetheless, establishing uniform baseline handling protocols can help keep all team members and stakeholders on the same page regarding how particular collections should be handled and what special considerations to account for when evaluating individual items from that collection. This must be done in close consultation with the conservation team of the institution, drawing on their expertise and experience in the proper handling of Cultural Heritage items.
This interaction between the conservation team and digitization team should be collaborative. Digitization teams often have only cursory educations and backgrounds in conservation, and conservation teams often have only cursory understandings of the digitization process. When mass-digitization is an institutional goal, there must be a concerted effort to promote cross-pollination between the two teams. Not only will the digitization team develop a better understanding of material handling, but the conservation team will learn the practical effects of certain handling restrictions. In some cases, a minor handling accommodation can profoundly impact the utility and speed of digitization. For instance the quality and speed of digitizing a manuscript collection can be increased by allowing it to be digitized by a PSI-limited operator-controlled gentle contact with a glass platen; such a system can greatly increase the readability of the digital object created by providing a partial flattening of the page, and increase the capture rate by 10X or more (e.g. simultaneous capture of both pages in one pass using a DT BC100 Book Capture System vs. focus stacking on a general-purpose non-contact copy stand).
“At the University of Illinois at Urbana-Champaign Library the communication between digitization and conservation is really developing into a robust two-way conversation where we are educating each other. Conservation is always working with the digitization team to tell them about physical limitations due to bindings or other restrictive formats, what we can and can’t fix, and making them understand why we can’t fix something. Digitization staff have also become more confident of their judgement during the digitization process – they know when to know to stop and call conservation. Likewise it’s helping us go in and look at their cameras and understand their workflow, how are they handling materials, how are they propping the books open, what sorts of straps and weights they are using, and how those tools react with the object so we can better work to conserve our materials anticipating that sort of use.”
– Jennifer Hain Teper, Head of Preservation Services, University of Illinois at Urbana-Champaign
The purpose of such interaction is not to pressure the conservation team to provide more liberal object handling protocols than they are comfortable with. Indeed, this would be anathema to the primary goal of a cultural heritage institution; the safety of the collection must always come first. Instead, this cross-pollination should seek to provide both teams with greater knowledge, such that the conservation team can provide handling protocols that keep the collection safe without being needlessly restrictive, and the digitization team can understand the protocols themselves, as well as the underlying reasons for their details.
“Our students found a journal with pretty wallpaper samples that they were touching and admiring. They wondered what we should do with the book, after it had been disbound and digitized, because it was considered non-unique. I suggested they consult with the Head of Conservation. The Head of Conservation read the article title, ‘The Dangers of Arsenic in Wallpaper’ – arsenic was used to make vibrant, colorfast inks in the Edwardian/Victorian era – and she advised the students to wash their hands.”
– Lawrence Wentzel, Associate Librarian, University of Michigan
Some institutions may not have a staffed conservation position. In that case it may be helpful to explore the possibilities of reciprocal site visits with a neighboring or associated institution that does, paid outside consulting, or attendance at an relevant conferences. Any effort to foster cross-pollination with individuals or groups with conservation experience is likely to be rewarding.
Contact vs Non-Contact Scanner
As a matter of definition, Contact Scanning means any type of digitization that requires, at any stage in the process, something to come in contact with the object with the exception of using hands (gloved or ungloved) for the basic handling of the object. This includes glass platens, straps, magnets, bars, and corner holders.
There are two types of contact scanners:
- No PSI Limit (aka Uncontrolled Contact): In most systems, the amount of pressure exerted during contact is not measured and there is no method to hard-limit this pressure. For example, when using a spring-based cradle the amount of pressure exerted on the object will vary depending on how thick the object is. An item with a 4” binding will compress the spring more than an item with a 2” binding, and will thereby experience more pressure since springs increase in force the further they are compressed.
- PSI Limited (aka PSI Controlled Contact): Some systems provide a built-in or optional add-on provision for hard-limiting the pressure of any contact with the object. For instance, the DT BC100 Book Capture System has an optional pneumatic cradle used to raise a bound material against a statically positioned glass V platen. An adjustable valve limits the maximum amount of pressure that can be exerted upward during this raising motion, and a self-correcting lateral sliding mechanism and in-cradle object cushion ensure this pressure is spread evenly over the object. Such a limit does not inherently eliminate the potential of damaging an object, but it does give the technician and curatorial staff an objective method to measure and limit the pressure exerted, offering some level of protection.
When using a No PSI Limit system, it is especially important for the conservation team and digitization technician work closely together. The technician should demonstrate potential ways the system can be used, and received immediate feedback from the conservation team as to which variations conform to the required handling protocols for a particular collection.
In the case of PSI Limited systems, an institution-wide objective maximum can be set for different classes of collections. The request to digitize a particular collection or object can be accompanied by a specific and relevant PSI limit which can then be objectively followed by the digitization team. Such objective limitations are also useful when outsourcing digitization to a third party vendor.
The exact manner in which a contact system operates is also be critical in determining what materials it can safely handle. Ideally, contact should be entirely technician-controlled; robotic and automatic handling are not able to adapt to changing conditions in the same way that a trained technician is. For instance, in a bound object, there may be an isolated page which is damaged or torn which requires more careful handling. Such a case is easily identified and handled by a human operator but is potentially vexing for a robotic system.
Contact systems which use a pivot point are not as desirable, as the contact will roll unevenly across the object.Contact should be homogeneous across the surface of the object instead, as is the case with the RGC180 and BC100.
The use of a vacuum system has both pros and cons.
- Benefits: Objects which are flexible but tend to curl, roll, or otherwise deform can be held in a flatter state by means of vacuum. The vacuum table will not visually obfuscate the object, unlike systems using weights, magnets, or restraining belts/bars.
- Disadvantages: Some material is sufficiently breathable that air from the vacuum will pass through the object itself, dragging with it any dust and other undesirable particulates. These risks can be mitigated by adding an appropriately sized air filter to the room, and shortening the time the vacuum is on. For example, a policy that the vacuum is only engaged immediately prior to the final capture would limit these exposures. More problematically, some materials are not pliable enough to be usefully flattened by a vacuum, as vacuum pressure is limited by nature to 15 psi.
Heat / UV from Lighting
The desire to keep collections at their native storage temperature is nearly absolute across institutions. This should not change during digitization. Scanning/digitization hardware should not expose the object to meaningful heat (or temperature changes in either direction for that matter). In modern reflective digitization, this is not problematic, as the industry-wide movement to strobe and LED lighting has eliminated the enormous heat generation of tungsten-based lighting. Furthermore, most professional strobe systems include strong UV filtration, which greatly reduces concerns about UV damage; a handheld UV meter can be used to confirm that a given light source is safe, or lighting can be purchased from a company that specializes in cultural heritage imaging and understands these considerations.
Selection of a system for digitization of transmissive materials is constrained by desire for both high CRI lights and a continuous light source in close proximity to the object to provide guidance for object handling. Many institutions shoot transmissive materials directly on a lightbox, exposing the material to heat. Instead, it is desirable to raise the transmissive materials away from the lighting surface. This is the approach taken with the DT Film Positioning System, which ensures the object is exposed to only minimally raised temperatures while providing rapid preservation handling.
Cropping & Inclusiveness
Guidelines need to be developed regarding the cropping and inclusion of the object, before digitization commences. The most common guidance in Cultural Heritage imaging is to be quite conservative in both regards, a standard which can be referred to as “full object inclusion.” For cropping, this means all four edges of a rectangle (or all edges of a non-rectangular object) are included in the capture, even when there is no meaningful content at or near the edge of the object. For inclusiveness, this means imaging every object in a group regardless of content. For instance, shooting every page of a bound material, even when the page is blank or is a duplicate of another page.
Many institutions also include an Object Level Target [see Object Level Target (OLT)] within the frame. When possible, these Object Level Targets should be included in the PDO, even if other non preservation derivatives (aka access copies, presentation version, etc.) crop them out. Sophisticated workflow software, such as Capture One CH, can be used to automate the process of creating both types of output with their respective crops.
The background against which an object is captured is important for several reasons: visual perception, workflow, and transparency handling.
The background against which an object is viewed has a strong influence on the way the viewer visually perceives the object. This is a topic far too broad to discuss in this document, but should be carefully considered. While it is possible to remove an object from the background digitally, it is a time consuming and imperfect process that is not broadly accepted in the Cultural Heritage Community. Therefore, it is very important to consider what background is used prior to the initiation of digitization.
In a workflow including automatic cropping such as in Capture One CH, it can be useful to ensure contrast between the object and background. Workflow considerations like this should never supersede the more important questions of correct visual presentation and other curatorial considerations. However, when all else is equal, a background which has higher contrast with the outer edge of the subject will work more easily with autocropping. For example, shooting a white document on a gray or black background will require fewer manual corrections when autocropping.
As some objects are not fully opaque, consideration should be given for what background such transparency should show through to. For instance, digitizing a single layer of carbon copy paper against a black background rather than a white background may significantly increase legibility of the writing. This is also true when digitizing bound material; a thin page may “leak” part of the next page’s content unless a blank sheet of paper is inserted as backing.