1. In a well-ventilated area, follow package instructions to carefully mix concrete and water together until smooth. Wear a dust mask and rubber gloves during this process.
2. If desired, stir in liquid concrete color.
3. Carefully pour concrete into an 18-ounce plastic cup until 2/3 full. If desired, pour multiple shades of concrete to create a ombré effect.
4. Place a 9-ounce up inside the concrete-filled cup and push until concrete has risen to the rim of the larger cup. Make sure the cups are not touching.
5. Tap the sides of the larger cup to remove any air pockets in the concrete, then use a piece of duct tape to hold the cups in place. Let concrete cure for at least 24 hours (follow package instructions as more time might be needed for concrete to fully cure).
6. Once dry, remove the small cup, then use pliers to carefully cut and remove the larger cup from the exterior. Sand edges to smooth rough spots, then wipe clean and use as a pencil cup, candle holder or planter.
Note: Concrete is not safe for food or drinks.