An apparatus used to calibrate microtiter plate readers. The apparatus includes one or more structures having two exterior surfaces wherein one of the exterior surfaces is coated with a coating selected to establish on that surface a reflection loss that mimics reflection loss at an air-liquid interface, and the other of the two exterior surfaces is coated with a coating selected to establish a reflection loss on that surface that mimics the reflection loss at a bottom surface of a microtiter plate. The apparatus may be a single layer, a multi-layered composition or a container. The apparatus is an artifact that may be used to calibrate a plate reader by mimicking a solution-filled microtiter plate. The artifact may be used for a plurality of liquids, including water. The artifact produces reflection losses more closely mirroring reflection losses expected for a liquid-filled microtiter plate well.