There are two ways that undermount double bowl bowl sinks are made.
The bowl can be drawn (pressed) one bowl at a time and then the bowls are trimmed and welded together to make a two bowl sink. The sink can also be constructed in a single pressing (called annealing) creating both bowls at one time. This eliminates the cost of trimming the bowl and the welding step making the sink much cheaper.
The primary disadvantage of the single press method is you are stretching two walls out of the center of the sheet steel. Below are pictures of a pressed single bowl before it is trimmed for welding. Notice how much steel has been stretched out of the sides of the bowl. If sink is made in a single step that steel needs to be stretched out of the center rail making them thinner.
Single pressed bowls will be lighter than welded bowls if pressed from same steel. Single pressed (annealed) bowls are more likely to have minor imperfections in the corners between the sides and bottom. These imperfections will show up as waves or dimples.
Copyright 2014 Tom Robinson