When changing weather “takes away” the green from autumn leaves, they turn red and yellow. When bare wood is finished, deeper colors appear.
With color, what you see isn’t always what you get. Discover the reasons why in the February edition of the Science Bag Lecture Series at the University of Wisconsin–Milwaukee (UWM).
In “Hidden Colors Revealed” UWM chemist Alan Schwabacher will show various ways that color can be present, but not visible – or uncovered. The interactive lecture is held every Friday this month at 8 p.m. and on Sunday, Feb. 13, at 2 p.m.
Schwabacher isn’t a magician, but he will make a white cloth made of fiberglass invisible before your very eyes. He does it by submerging the cloth in a liquid of the same index of refraction. That’s the relationship between the angle of light as it passes from one transparent medium to another and the extent to which it is refracted, or bent. When two materials have the same index of refraction, the light is not refracted and the boundary becomes invisible.
Certain chemical reactions can also eliminate color. Schwabacher will demonstrate how substances can change from one color to another by removal of “obscuring” colors. To demonstrate this, he will fill a flask with water from the tap and pour it from one apparently empty flask to the next. Each time the same water is poured into the next empty flask it will change color – from magenta to yellow to red to blue.
On the flip side, Schwabacher will also show some ways that colors caused by chemical reactions can form. He also will show how colors can hide by being mixed with other colors.
Though they have wavelengths on the invisible scale, colors like ultraviolet and infrared have effects in the visible world. Ultraviolet plays a role in causing sunburn and infrared helps us to see whether insulation is effective.
The Science Bag presentations are held in room 137 of the Physics Building, on the corner of Kenwood Boulevard and Cramer Street. The Science Bag is for the curious, ages 8 and older, and is free.