I sometimes get asked, how to mark turtles by people who have many and would like to be able to tell them apart. It is generally not recommended to use ANY paint on smaller turtles. Many paints have some toxins in them, and all paints will cover the shell in such a way that no air can pass through. I have seen larger tortoises marked with small dots of paint by people who know what they are doing. Here are some ideas on what to do: * All turtles' shells and markings are unique for indivuduals. For sliders and many other turtles and tortoises, you can memorize (or make labeled drawings or photographs), especially of the plastron (bottom shell). Many turtles/tortoises have nicks, malformed scutes, color splotches, scars, or other natural markings that distinguish them from the rest. * Use duct tape marked with paint or a marker pen. * Use a permanent marker and mark the turtle with a very small mark. * If you are going to use paint, make sure it is non-toxic, and use as little as possible. * I wonder how well nail-polish would work. It's non-toxic (since it's OK to put it in little baby's nails), but it might chip off after a while. However, any paint will chip, scrape, or grow off after a while. * Never cut, notch, or drill the shell, since it is living bone. * Or, best, but hardest: spend a lot of time staring at your turtles, until you can tell them apart. They ARE all different. (I know, this is not easy, especially if the turtles are of similar size and live in a pond where you don't see them a lot. Just thought I had to mention this...) This is not much, but maybe it gives you some ideas...