This post was written by Katharine.
This tool is a dream to avoid unwanted creases when pressing curved seams such as darts. Its name comes from the shape of a baked ham joint. You place the seam being pressed over the best fitting curve for perfectly smooth results. One side is wool and the other is cotton. You press on the side of the ham made of the same material as your seam. I filled mine with scraps of woollen fabric to give a nice heavy surface. Wood shavings are a good alternative as they avoid a lumpy finish.
I used these instructions to make one. It includes further patterns and I confess into pressing my Dad into making the seam board (which could merit another, ‘how did I ever sew without…’). There are more guides to making a tailor’s ham here, here and here.