Stereolithography is the oldest and one of the most common methods for printing. It prints by using either one or two lasers focused at a pool of photosensitive liquid. When the laser(s) focus on one point at the top of the pool, the liquid solidifies. This happens a layer at a time, each layer being typically about 0.1mm thick. Each time the machine goes to print a new layer, the bed moves down and more photosensitive liquid is poured in.
When the model is done printing it goes into another machine to be cured under an ultraviolet light.

Stereolithography SLA Stereolithography SLA 2

 

Advantages

• The machine is very accurate and the vertical step size is small. This is good if you are looking for exact specifications.

Disadvantages

• The models can’t be handled straight out of the printer, as they need to be cured first.
• Support structures must be printed depending on the specifications of the model, but because of the nature of the machine the supports must be made out of the same material as the model. This means that you have to cut them off manually after curing, which can leave artifacts (I have a first hand experience with this one).