Labs, taxidermy stores, and movies about mad scientists are populated with semi-translucent creatures in jars. These are commonly called "diaphonized" creatures, and they've been in real labs since the 1970s. But what started as a way to get a good look at skeletons became art.
The first step in the diaphonization process is a long bath in trypsin. Animals in nature also enjoy this bath, but they generally enjoy it from inside the stomach of another animal. Trypsin is a digestive enzyme that breaks down proteins. Dump trypsin in milk, and it will attack the protein called casein. Casein doesn't just add nutrition to milk, it adds color. Rip it to shreds with an enzyme, and the milk becomes translucent. Put trypsin in a jar of fluid containing a dead mouse or lizard, and the proteins there become translucent as well.
A completely translucent animal is not particularly interesting or useful, so to complete the diaphonization we turn to dyes. Most diaphonized animals are dyed with either alizarin red or alcian blue. Alcian blue is a by-product of the acid-making process, while alizarin red is a natural dye derived from a flower. The only thing they have in common is an affinity for calcium — whene they encounter it, they stick to it. Because the bones are filled with calcium, they take the dye and stand out red or blue in the translucent remains of the flesh.
Some diaphonized specimens are strange and beautiful. However, most of the animals that go through the process are fairly gruesome-looking. If you're making a horror movie, or just want to ensure that your friends don't come over and eat all your food, they could be ideal.
You can see some incredible diaphonized animal images here.