molding-urethane.md

@@ -92,7 +92,9 @@ The castable urethane we use here is a [Clear Flex](https://www.smooth-on.com/pr
 
 If you want to color the sample for imaging purpose, you should use [So Strong](https://www.smooth-on.com/products/so-strong/) dye. In the following walkthrough of the casting method, we lightly tint our sample green because that coloration usually optimizes contrast in a polariscope.
 
-More aggressive addition of dye can simulate the effect of using an optical filter or illuminating with monochromatic light.
+More aggressive addition of dye can simulate the effect of using an optical filter or illuminating with monochromatic light. In the image below, we show sets of particles that are (left to right) darkly dyed, lightly tinted, and clear.
+
+![DSC_2286__1_](uploads/b0d184dc3c2c844e65d2bdc71da15997/DSC_2286__1_.jpg)
 
 In this case it is helpful to keep in mind that the stress-optic coefficient is a function of wavelength: coloration, in addition to stiffness and material thickness, controls the resolution and dynamic range of your photoelastic measurements.  Longer wavelength (redder) light produces fewer fringes for the same strain than shorter wavelength (bluer) light.