This visualization maps when objects were made, and when they were acquired by the museum. You can adjust your view by changing the yellow dates. The brightness of the yellow date bars indicates a "completeness" of the object's catalogue record. The brighter the yellow, the more fields in the record contain a value. So, we don't know much about objects represented by the darker yellow bars.
Try an example? 0-150, 1850-1900, 2000-2014.