Tracking LILIS

By May 18, 2020May 19th, 2020Printmaking, Research

Tracking LILIS (Light Induced Low-Intensity Staining)

In November, 2016 Aardenburg Imaging & Archives began a series of light fastness tests using an extended testing protocol to study the phenomenon of light induced low-intensity staining (LILIS). These samples can be found in the Aardenburg light fade database by filtering the records on batch = “P” and also batch = “Q”. Both batches have been tested with the extended protocol. In the Conservation Display Rating column, look for the asterisk and the word “LILIS” to indicate those media which are impacted by the Light Induced Low-Intensity Staining (LILIS).

LILIS is caused by the light induced degradation of optical brighteners (OBA) incorporated in modern media, and it also correlates with the combined presence of both OBAs and titanium dioxide (TiO2). The concentration of OBAs and their location(s) within the media coatings are also important factors. LILIS manifests as noticeable yellowing of the media white margins and image midtones and highlights beyond what can be attributed merely to the loss of fluorescence as the OBAs degrade upon exposure to light. 

The reports in this study have recently been updated to include 20 Megalux hour samples measured again after 3 years dark storage time since the initial 20 Mluxhr reading, 50 and 100 Mluxhr samples after 2 years, 200 Mluxhr samples after 6 months, and lastly, the dark stored control samples remeasured at 3 years total elapsed time since the original reference measurements were made. The Aardenburg Conservation Display Ratings for each printer/ink/media combination have been revised further downward where applicable due to continued yellowing of the media. Testing is ongoing.

SUMMARY:

1)  The widely held assumption that modern media containing optical brighteners merely revert to their “natural color” as the OBAs fade is demonstrably false! Additional yellowing over time becomes easily noticeable.

2)  Additional media yellowing in samples exhibiting LILIS continues even after two to three years in dark storage, but the rate of yellow stain formation at ambient room temperatures is finally beginning to slow.

3)  No occurrence of LILIS has been observed with OBA‑free media!

4)  All unexposed control samples remain in excellent condition after three years in dark storage, i.e., no noticeable changes, thus proving LILIS is light‑induced.

5)  Resin coated (RC) photo media are the most commonly used media for photo printing yet no OBA‑free RC photo media exist today. This reality makes the recommendation to choose OBA‑free media for archival printing easier said than done.

6)  For media containing OBAs and with artistic, historic, and/or sentimental value, 10 Megalux hours total light exposure accumulation over time is an appropriate guideline for conservation display purposes no matter how lightfast the image forming particles, dyes, or pigments are.

Our goal for 2021-2024 calendar years is to once again use the Aardenburg extended testing protocol to evaluate popular non RC gloss/luster media, i.e., the so‑called “Baryta” and baryta-like traditional fiber fine art media. Careful comparative choices in this media category should help us to better understand the relationship between OBAs and TiO2 with respect to LILIS because this category of media contains OBA-free, OBA with TiO2, OBA‑free with TiO2, and OBA without TiO2 formulations. This category of papers has also undergone some supply chain necessitated reformulations of various popular brands, thus another reason for a new round testing.

Kind regards,

Mark McCormick-Goodhart
Director, Aardenburg Imaging & Archives

The data in this round of reports represents 4 years of testing using the Aardenburg Imaging Extended Testing Protocol. Membership and access to the data is free. Donations fund the work. For our continued research, we are asking that you consider a $10 contribution. If half our membership donates $10 each, a full year of testing will be funded!

This data is not available anywhere else. In the case of LILIS, a lot of modern media exhibit this yellowing, and yet these materials are being marketed as “archival.” The manufacturers should take notice and offer more products that have been screened for LILIS.

The good news is that there are popular media on the market today which don’t exhibit this yellowing issue, and Aardenburg Imaging publishes data to help you chose. If you are printing and using a lot of expensive materials in your work, then this information helps you choose more wisely. Ultimately, then, you will have more confidence in the product that you are making, the finished print.

The story of modern inks and media and their archival qualities is ongoing. Together, with your support, we can continue to tell that story. We thank you for your support!