Digital scores in the Solti Collection

1. Locate the secret URN for the digital copy (check the holdings record in Alma, 856 |u ).
2. Open the Mirador file.
3. Save the desired page at the greatest possible size.
4. Open the page in Photoshop.
5. Invert the image (Image → Adjustment → Invert).
6. Zoom in (ctrl +).

At the Weissman Preservation Center, there is equipment that has the capability to image with different wavelengths of light: a VSC (visual spectral comparator) uses multi spectral light sources to examine documents and is typically used to improve legibility and characterize properties of supports and media. Retrieve the scores, mark the pages you wish to have imaged in the VSC, then transfer them to WPC. 

Imaging Services is also a good resource for issues like this.