Gak may be the internet’s favorite slime recipe. If you look up “slime recipes” on Google, you’re bound to find this one. Gak is stretchy, durable, and fun for all ages. Also, it makes a great stress reliever.
*GET AN ADULT*
Do not taste or eat gak. Exercise caution with boiling water.
- Elmer’s All-Purpose white glue (Amazon link: Elmer’s Glue)
- 20 Mule Team Borax (Amazon link: Borax)
- Food coloring (optional). (Amazon link: Food Color)
- Zip-lock storage or freezer bag (Amazon link: Ziploc Bags)
- 2-Liter bottle
- Popsicle stick for stirring (Amazon link: Popsicle Sticks)
- Disposable plastic cups (Amazon link: Plastic Cups)
- Narrow-mouthed glass bottle (a Snapple iced tea bottle is ideal). (Amazon link: Snapple Iced Tea)
- Microwave oven or other heat source
- Microwave-safe container or beaker
- Permanent marker (Amazon link: Sharpie Permanent Markers)
- Water-based marker (Amazon link: Sharpie Water-Based Markers)
- Eye dropper (Amazon link: Eye Dropper)
- Pour 1/4 cup (60 ml) of Elmer’s glue into a plastic cup.
- Add 1/4 cup (60ml) of water to the glue and stir thoroughly.
- Add a few drops of food coloring (optional) and stir thoroughly.
- Label an empty 2-Liter bottle as “Borax.” Add 1/2 cup (120 ml) of 20 Mule Team Borax powder to the bottle. Fill the bottle halfway with water, and shake vigorously for several minutes. This is your borax solution. Don’t worry if the borax doesn’t all dissolve.
- Add 3 tbsp (45 ml) of the borax solution into an empty cup. Using the eyedropper, add this solution a little at a time to the glue-water mixture. Stir with a popsicle stick. As you stir, the mixture will clump onto the stick. DO NOT add too much borax solution. If you do, the gak will get too stiff.
- Remove the clump from the popsicle stick with your fingers. Rinse off the remaining water. Then, work the gak with your hands until it becomes less sticky.
Try using a 1:1 ratio between glue and water (Steps 1 and 2) to make more gak. For example, combine 1 cup (240 ml) of Elmer’s glue and 1 cup (240 ml) of water.
- Attempt to pull the gak apart slowly. What happens?
- Now attempt to pull the it apart rapidly. What happens?
- Try to bounce it on the floor. Are you successful?
- Poke it quickly with your finger. What happens?
- Try to determine if it is a solid or a liquid. If left on the table, what happens to its shape? If it assumes the shape of its container, does this make it a solid or a liquid?
- Cut off the bottom half of a 2-Liter soda bottle and invert it so it acts like a funnel. Prop it up between two stacks of books so it is directly over a cup. Place the gak in the funnel and record the time it takes to reach the cup. Is the flow rate a good indicator of viscosity? Try varying the recipe to see how this affects the flow rate.
- Place your gak on a newspaper and press down firmly. (This works best with non-colored gak). Does the newsprint appear on the gak? Repeat with other types of print, such as a photocopy. Does the toner appear on the gak? Test a page from an inkjet printer, and then try a page from a laser printer. What happens?
- Write on a piece of paper with a permanent marker. Press the gak down on the writing. (This works best with non-colored gak). Does the ink appear on the gak? Repeat with a water-based marker. What happens?
- You can design your own colorful gak by drawing on it with markers or paint. Experiment to see what gives you the best results.
- To demonstrate the fluid-like properties of your gak, try this: Fill a Snapple bottle (or any narrow-mouthed glass bottle) to the brim with boiling water. Using a potholder to hold the bottle, pour out the boiling water. Quickly place a ball of gak on top of the bottle. Press it down a little so it makes a tight seal. Plunge the bottle into a bowl of cold water and observe the gak. It appears to get “sucked” into the bottle!
- Try blowing slimy bubbles! Wrap the gak around the end of a straw, then blow gently and slowly through the other end. It is important to make an airtight seal between the slime and the straw. With practice, you can blow slime bubbles the size of a basketball!
- Store the slime in a zip-lock bag.
Elmer’s glue is mainly composed of a polymer called polyvinyl acetate. (A “polymer” is basically just a long chain of molecules). Also, Elmer’s glue has a greater viscosity (resistance to flow) than many liquids, but is not nearly as viscous as slime. The borax solution causes polyvinyl acetate molecules to “cross-link”.
You can compare “cross-linking” to spaghetti.
After cooking a batch of spaghetti, it starts to dry if you leave it out for a while. Then, as the water evaporates you start to see spaghetti strands stick to each other (see Figure 2).
Similarly, the borax (sodium tetraborate) molecules dissolve in water to produce borate ions, which act like the “joints” you see in Figure 2. In this case, however, the ions hold together “spaghetti” strands of polyvinyl acetate molecules. This makes for a much more viscous solution, (unlike the Elmer’s glue in Figure 1), because the borate ions firmly link the polyvinyl acetate molecules together.
Gak is an example of a non-Newtonian fluid.
According to Isaac Newton, the viscosity of a liquid depends only on temperature. But one can alter the viscosity of a non-Newtonian fluid, such as gak, in several other ways besides changing its temperature. If you pull the gak apart slowly, it forms long thin strands. But if pulled apart rapidly, it breaks. It bounces somewhat when forming it into a ball and dropping it on a hard surface. If poked quickly with a finger, the finger will bounce off. But if poked slowly, the slime easily absorbs your finger. Other examples of non-Newtonian fluids are quicksand and Silly Putty.
Since gak assumes the shape of its container, it is a liquid, not a solid. Solids have a definite shape; liquids do not. However, the slime is a very slow-flowing liquid, which is classified as one having a high degree of viscosity.
Water-based ink tends to transfer more easily to gak than permanent ink. Also, water-based ink tends to run when drawing on gak. On the other hand, permanent ink tends to make a more lasting impression.
When emptying the bottle of boiling water, air inside the bottle heats up. Remember, air expands with heat. As a result, this expansion forces some air out of the bottle. Once the bottle is cool, air within the bottle is also cool. Keep in mind, when air cools, it contracts. Because some air escaped the bottle earlier, there is now less air pressure inside the bottle than outside the bottle after cooling. Consequently, greater outside air pressure pushes the gak into the bottle. Hence, the gak was pushed into the bottle, not sucked. In conclusion, slime is a non-Newtonian liquid, which can be molded to fit into its container.
Want more slimy recipes? Check out these links: