Although many chemistry demonstrations are proposed in educational literature, there are hardly any studies on how demonstrations should be set up in order to support students' perception. Against this background, the aim of the present study was to present and test setup principles for chemistry demonstrations, with regards to indicators of students' visual attention on the relevant equipment in a demonstration. On the basis of the Gestalt principles, we carried out an experimental double-blind eye-tracking study. We set up six demonstrations that each corresponded to one Gestalt principle ("Gestalt setting") and six demonstrations that explicitly violated one principle ("control setting"). There were 146 students from secondary schools randomly assigned to watch a demonstration either in a Gestalt or a control setting. Visual attention was captured using an eye-tracker (eye-follower 2.0). The total fixation count, total fixation duration, total mean fixation duration, and time taken to fixate were analyzed. The results show that demonstration setups have an impact on visual attention, with small to medium effects for each Gestalt principle. In order to support learners watching a demonstration, educators should carefully plan the setup with regard to their concrete learning goal(s) and the equipment they want to focus on. In particular cases, educators will have to decide purposefully between competing principles.