This is my attempt on OIL based color sensory bag. Heat sealed. I have tried to seal with clear duct tape, but the seams inevitably start to leak.
Step 1: Materials and Tools Required
Thick plastic bag
(the thickness and texture/feel is very similar to that used in greenhouse sheeting )
Oil - preferably edible oil or baby oil
food color - water based
piece of cardboard or flat surface (heat resistant),
container for food color dilution
Step 2: Get Ready Your Working Place.
I did this on ironing table, in any case. Place some thick cardboard piece (or other flat heat resistant material). Then on top of that put some aluminium foil.
Set your iron to higest heat (III or for coton ironing).
Dilute food coloring, because some of undiluted colors (blue) look too dark. The best way to tell approximate needed dilution is to test it against bright light (as in picture, and that is the amount of color you'll need).
Cut your bag to necessary size, if needed.
Step 3: Putting All Together.
Add a little bit of oil in plastic bag, start by adding little amount (i did no measuring, just by feel), then add color. Best to use one color in one bag, because the color will mix together enyway.
Squeeze out air, you can leave some air in** thats fine too, just don't let the oil reach end of the bag where the sealing will happen, that will prevent a good sealing.
Fold the end of the bag and place it between folded aluminum foil. The foil is there to protect iron from plastic bag sticking to it.
Then use the iron to heat seal the bag - hold it for few seconds - sealing/melting happens fast.
And you are done.
** - air in the bag can be as a third substance (medium) - air, water and oil.
Step 4: Enjoy
But be careful, kids still can bite through the plastic or pinch holes with their sharp tiny fingernails :).
You can tape it with clear duct tape for better protection.
Still parental supervision needed, be safe.
Some people add sparkle dust, or smal toys, but that also can lead to punctured bag.