Only use Gatorade or G2 bottles for the sensory bottles they are a heavier plastic so they hold up better and keep a unison look so everything looks good. They come in different sizes you can find smaller ones for small hands if you need to.
Make sure to ALWAYS seal your bottles securely! I cannot emphasize this enough. Unless you want your bottle opened and the contents poured out. SEAL IT… with glue. Duct tape can be peeled off by a determined kiddo. Glue is much harder for them to open up.
Mixing Color Bottle
You will need colored lamp oil (do not try to color the oil you need to buy it with the color already added) for the oil portion of this bottle, other oil will not work. Color water using food coloring. Next pour colored lamp oil on top of your colored water. So the bottle should be half colored water and half colored lamp oil. Seal the bottles and shake. The colors will mix and then separate again and again. This is by far my preferred way of making these bottles.**Lamp oil is very dangerous if swallowed, make sure you seal your bottle very well.**
Color vegetable oil with powdered tempera and add to a water bottle. Color water with food coloring and pour into the bottle. Colors will mix to form secondary color when shaken, then separate again when undisturbed.
All three pictures are using the second method
For a list of ALL my amazing DISCOVERY BOTTLE IDEAS click the link or the image below