This simple colorimeter was inspired by this one:
The webpage above contains a great suggestion on how to use the colorimeter with students too.
The cuvette rack I've published earlier is used by students to keep the cuvettes safe when using this colorimeter. I use it at work for high school students. They try to determine the concentration of brilliant blue (E133, CI 42090) in mouthwash after making a calibration graph based on a known solution of brilliant blue. The instrument is primitive, yet demonstrates the principle of colorimetry beautifully. The simple, primitive construction of the instrument opens up for interesting discussion and suggestions for refining the experiment, enhancing the learning experience. The experiments it can be used for combines maths, physics, electronics and chemistry nicely. I really like this little gadget. It's a gem.
I've added a PDF with pictures of the assembly process in the download section. Apart from the material for the box itself, you'll need an LDR, a bright white 5 mm LED, a 220 Ohm resistor, about 20 cm of connecting wire, a pair of short metal rods or nails to solder the probe leads to, a 9V battery clip with soldering leads and a pair of multimeter probe leads. You'll also need a pair of slim nosed pliers, a wire cutter, a wire stripper, a small hammer for the rods, a soldering iron, soldering lead, at least 4 cuvettes, colour samples, and a multimeter for reading the colorimeter once it's finished.