Knowing little about jewellery making and pottery, I imagine these activites to require quite different work areas, at the very least once will be more messy than the other. One wouldn't switch from handling clay directly to working with metal or precious stones. Still, those places can inspire each other, and perhaps some jewellery incorporates pottery or the other way round. The place to sit I'd like to design for this person is a studio for making both things. It needs to be two separate work areas, side by side, so there is a visual link, with some division to avoid dirt spilling over. The person did not talk about light, but I'd like to think this place to be flooded with natural light, both work areas should face a big window floor to seeling and a beautiful natural scenery outside. Since they like the colour blue, I'd include subtle elements of blue in the room, in the curtains and in the chairs to sit on. I wouldn't overdo it, because I imagine there will be already many shades of blue in the materials they work with. The walls are white and the floor is wooden, perhaps a bit creaky as you walk on it.
The pottery workbench has a simple with steel legs and little wheels and a leather-covered cushion so it's easy to clean. It should be easy to move around a bit and swivel while working. You can also tilt the seat to adjust it to a comfortable position. It does not have armrests or a backrest as you're using your arms and probably tend to bend slightly foward while doing pottery. I also encourages a straight posture.
The jewellery workbench has a wooden chair, with armerests and a backrest. It doesn't have wheels because you might have to do very fine and detailed work and you don't want your chair to move about. The seating area of the chair is wooden too, slightly curved downwards for a more comfortable sit. The backrest has round wooden bars. The chair is old and used, the wood has a dark colour.