From ARTstor:
Please be advised that ARTstor will be performing an upgrade to our systems beginning on Saturday, January 26th at 11:00 PM EST and concluding on Sunday, January 27th at 1:00 PM EST. While the upgrade is being performed, users will not have access to the ARTstor Digital Library.
During the outage, please consider using LUNA instead for your image needs. If you experience difficulties with ARTstor after 1:00 PM EST on Sunday, try clearing your cache. If that doesn’t work, please contact userservices@artstor.org.