Hi, Thank you for sending this wonderful exuberant mark from the back of a willow pattern plate. It was used by Swillington Bridge Pottery near Leeds. Even though the pottery was built in the late 18th century, ironstone type wares were not produced until c. 1827. There were many different partnerships running the pottery. By 1833, it was taken over by Reed & Taylor of Mexborough Rock Pottery. Many shards have been dug up from the site, but plates with willow pattern are the only complete pieces found. We would be happy to record your piece in the TCC Database with your permission if you send a good quality photo to me at the email address given here. Thanks for sending the mark!