By Betty Klem 
I’d like to share some of my favorite basic recipes for sensory activities that explore materials and the way they behave and react.  All of these are tried and true.  There are many newer recipes for potions and doughs.
Playdough
This is the standard for playdough and should be available in all early childhood settings.  The basic recipe is:
·         4 C flour
·         2 C salt
·         8 Tbsp. Cream of Tartar
·         4 Tbsp oil
·         4 C warm Water
Mix ingredients in a large pot.  The mixture will be runny.  Cook, stirring with a wooden spoon, at medium heat until the mixture pulls away from the sides of the pan and is the consistency you want.  Knead.  There are many variations on playdough.  To color it, add food coloring or liquid watercolor to the water before cooking.  You can scent it with essential oils or extracts.  When I was teaching, we found we needed to make a new batch weekly, and my grandchildren love to speculate on what color the playdough will be this week.  You can also add stuff to the playdough:  try glitter, coffee grounds, sand, anything that will change the texture.
Silly Putty
Another old favorite.  There are all sorts of varieties of this weird mixture.  You mix liquids and get a kind of semi-solid. 
Mix:  2C white glue, 1/2 C water, and food coloring or liquid watercolor.
Mix:  1/3 C water with 1 tsp powdered borax.
Add borax mixture to glue mixture a little at a time.  Stir until the liquid is absorbed.  Do not add more borax.  It may take quite a while to get everything mixed.  Store in a sealed container.  The children should wash their hands before playing with this–if you play with dirty hands, it gets very sticky and will mildew.  This product has unusual properties.  It will stretch, bounce, break, and more.  Experiment.  If you set it on the edge of a table, it will slowly ooze over the side.
Goop
Goop is simply a mixture of cornstarch and water.  Make a big batch–fill a dish tub or a texture table with it.  It doesn’t keep, so enjoy it freshly made. 
Add one part of water to one part of cornstarch.  Adding more or less of each ingredient will change the properties.  EXPERIMENT.  The cornstarch sinks to the bottom, and you can pick up what seems like a bare handful, but it will ooze between your fingers like a liquid.  Start with a tub of dry cornstarch and let the children help add water to it, colored if you want.  You’ll want to buy cornstarch in large sacks, not the little yellow boxes at the grocery store.  I have seen engineers get very excited playing in cornstarch because the properties are so unexpected.
Goop makes a big mess on the floor, but if you use it outside, you can hose it off.   If you use it inside, it dries to a powder, and you can sweep it away or vacuum it up.
To turn Goop into OOBLEK, use about one part cornstarch to three parts water and cook until thickened.  This has a very different feel than Goop.  It’s fun to divide the oobleck into parts and color them different colors.  Children add spoonfuls of 2 or 3 colors to ziplock sandwich bags, seal (a bit of duct tape across the seal prevents leaks.  Then squish and massage to mix the colors. 
Bubbles
This is a lot cheaper than buying bubble solution. 
Mix:  6 C water, 2 C Dawn, 3/4 C white corn syrup.  You could replace the syrup with glycerin.  Both make the bubbles last longer.  Stir until blended.  Try making bubbles with all kinds of objects–bubble wands, jar rings, your fingers.  We even used a hula hoop and a wading pool. 
Shaving Cream
You can do so much with Shaving Cream.  Squirt some on a plastic tray or a table and finger paint away.  You can draw in it, smear it, mush it–whatever you want.  You can sprinkle on powdered paint or spray or drop on liquid watercolor.  This is a great medium for marbling.  Add color and swirl to make designs.  Take a print by gently laying a piece of paper on top, then remove.  You can also add things to the shaving cream to change the textures.
Exploding Colors
These are two ways to play with color.
1.  Fill a tall, transparent container 3/4 full of water and float a thin layer of vegetable oil on the top.  Drop drops of food coloring into the oil, and watch what happens as the color passes through the oil and enters the water.  Beautiful!
2.  Fill a pie tin or other shallow dish with whole milk.  It works much better with whole milk.  Drop drops of food coloring on the milk.  Then, dip toothpicks in dishwashing liquid and touch the color.  The dishwashing liquid breaks the surface tension, and the colors swirl all over.
Ice Castles
This activity demonstrates how salt affects ice.
1.  Sprinkle rock salt onto a large block of ice.  Watch how the salt melts caverns into the ice. Drip color into the caverns.  Using pipettes or turkey basters, or even spoons to pick up the meltwater and baste the block can keep children enthralled. 
2.  Freeze water in various containers such as milk cartons, plastic storage containers, bowls, balloons, etc.  Dump them into the texture table or a tub.  Sprinkling with salt will cause the ice pieces to partially melt, then freeze together.  Add color and baste.
 Volcanoes
The old baking soda and vinegar mixture gets a bit of body and excitement here.  In a pitcher mix one part water and one part white vinegar.  Add in a couple of squirts of dishwashing liquid.  The dishwashing liquid gives the bubbles body so that they flow like lava.  Add red color if you really want “lava.”  This is really messy, but very cool since the stuff will flow up and out of the cups.  Have the children put a spoonful of baking soda into a small paper cup.  Then pour in some of your volcano juice.  Instant eruption.
Web Resources
Some so many people post cool science and art activities on the internet that my first suggestion would be that you go to Pinterest.  Look for science activities for preschoolers.   Since all of the events listed above are old tried and trues, I suggest you simply Google “science experiments for preschoolers.”  There are pages of them.  My recipes are all pre-web.