Antique 'ijsselsteentjes' and old bricks is the specialty of De Opkamer. By demolishing old buildings, old masonry stones are still regularly released, such as old 'waaltjes' and antique 'ijsselsteentjes'. The Opkamer has mainly concentrated old antique 'ijsselsteentjes'. In the past, heavy stones were expensive, especially for the poor rural population. Farms were mainly made with walls of clay. When a farmer had saved enough to be able to pay enough stones, these mud walls were replaced by brick walls.