Sad or flat iron of solid cast iron: 19th century

Sad or flat iron of solid cast iron with a hollow iron handle. The top of the iron has an illegible maker's mark in relief, 'PATENT' and '7'. The maker is possibly George Salter and Company. Sad irons were heated on trivets in front of open fires, or on the tops of closed ranges, or on specially-designed iron stoves in larger laundries. They were made in numbered series which related to their size, although there was no standardisation in the series between manufacturers.