This pottery is obtained in the Varrock Museum activity when cleaning Uncleaned finds. "By the looks of it," the archaeologists in the cleaning area tell the player, the pottery "was made by Zaros worshippers." According to the archaeologists, the pottery reinforce the evidence that Varrock was occupied by Zarosians before Saradominists.
The player places the pottery in display case 22 (which is directly in front of the stairs that go to the basement) to be rewarded with 10 kudos. Note that this display case is already occupied with other pottery instead of a note card.
The text accompanying the exhibit in the museum reads as follows:
Two distinct types of pottery have been recovered from the Dig Site, adding evidence to the two settlements on this site. The red clay pottery appears to be much older and occasionally has purple Zarosian symbols, while the Saradominist artefacts are usually of a lighter shade with blue decorations.