Ever since seeing it done on the Make: channel around 5 years ago, I've been intrigued by wet forming leather. I've tried once or twice before, but to no avail, undoubtedly down to the poor quality furniture leather I attempted to use. Recently, I happened to get a small leather offcut of quite significant thickness and quality, so I decided to revisit this project, to make a belt-mounted holster for my penknife.
I started by making the form, the male piece from a small offcut of pine that was the approximate right shape and the female part from a particle board offcut (not the best material, but it worked out fine). I rounded the edges and corners on a belt sander(80 grit), and followed that up with a smoothing on some 120 grit paper. I ended up using a piece of melamine coated chipboard for the female piece. This was not the best material by any means, and I don't think I rounded over the corners enough, leading to some wrinkles in the leather, however they are not very noticeable. I preceded to cut out the form, unfortunately snapping my coping saw blade in putting too much tension on it when cutting the corners, but aside from that, everything went smoothly. I also mixed up some wood filler and; filled in the holes in the male form.
After checking everything fitted together, I preceded to soak the leather in warm water for around half an hour and then clamped it in place. The wait began.
24 hours later, I demoulded and found that it had worked. The leather was nicely conformed to the mould and kept its shape. I traced a lip, and cut it out, before cutting a matching back piece. The leather had warped near the top of the holder, so I trimmed that straight. I applied PVA glue to the regions to be joined and clamped them in place. A few hours later, they were nicely held together, and so I marked out and drilled some small holes with my rotary tool to sew through. I used thick thread and coated it with wax to make it more durable. A simple saddle stitch took me only around 15 minutes, after which I tied it off.
I later cut a slot to make removing my penknife easier, and soaked the thing in beeswax to make it waterproof, and somewhat burnished the edges. I also cut two slots in the back to create a belt loop. I hope to someday revisit this and add a lid/flap to the holder, however, my penknife doesn't seem to fall out without it. The fit of the knife is quite loose, so that is something to consider in a second iteration of this design, as well as replace the two slits in the back with a strip of leather, to create a more durable and presentable belt loop.