RTI on Katib Khosru wa Shirin (Interior Cover)

This is video capture that explores highlight Reflectance Transformation Imaging (RTI) using the RTI Viewer (provided by Cultural Heritage Imaging - free downloadable software for view RTI captures).  This RTI session was carried out by Catarina Figueirinhas and Jessica Ebert.  To learn more about RTI visit the Lab's blog post on the subject: http://blog.thepreservationlab.org/2017/04/fun-with-photodoc-rti-edition-5/ .  

This is the Katib Khosru wa Shirin, an Archives and Rare Books collection item.  You can read more about this Persian love story, here.  This book was previously treated by Gabrielle Fox, conservator and local fine-binder.  The book is often used in classroom teaching and presentations, so it was chosen as a candidate for RTI (Reflectance Transformation Imaging).  We conducted three separate highlight RTI capture sessions; one of the embossed, gilt leather exterior cover, one of the an illustration where a significant amount of pigment was missing, and finally one of the interior leather which features pigmented paper decoration with gilt leather decoration over top of that (represented here in this video capture).    

This video begins with in the default mode, which allows the user to move the light position around the object.  Moving the light around the object at a severe 15 degree angle allows you to view the object under raking illumination.  Commonly used in conservation photographic documentation, raking illumination shows off the depths and disturbances in the surfaces texture of the object, hence why it is commonly used to illustrate tears and cockled in paper.

Using the specular enhancement mode, we are able to remove the color from the object and add specularity.  This really accentuates the differences in the surface texture of the brown leather cover and the pigment paper cut-outs.  Under magnification (captured using a Carson handheld pocket microscope and an iphone) you can see the difference in the follicle pattern of the leather, which you can also see in the gold leather work in the specular enhancement mode, and the fibers of the pigment paper.  The pigment paper ares have an overall softer, almost powdery texture to them, whereas the leather, while smooth, is heavily textured by skin's hair follicles.

The normals visualization mode helps to show the dimension of the surface, allowing the view to more accurately see what is concave and what is convex.  In this case you can see how the intricate gold leather work clearly sits above the pigmented paper areas and how the only the edge of the gold leather work is on the same level as the brown leather cover.

The diffuse gain mode is ideal for identifying areas of surface abrasion and deformation, such as the scuffs and scratches on the brown leather's surface, which under normal illumination are not as apparent. The diffuse gain mode also accentuates the areas where the cover has sustained damage to both the gold leather work and the pigmented paper sections.