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First, map out where you want the stenciled designs to go. Use a light-colored washable marker to make small marks so you know where to place the stencil each time. Place one hand firmly on the stencil to make sure it doesn't move and hold the can about 4 inches (10cm) away from the carpet to spray in the design. Purchase pre-made stencils from craft stores or make your own out of cardboard or thin plastic materials. It's best to use just one stenciled design, but you can combine two different stencils if you lay them out in a thoughtful way. For instance, stick to a single celtic design to be spaced out evenly across the center of the carpet or around the edges. You can also use different floral stencils for a smart, unique look. Use painter's tape to act as a stencil. Lay it out in stripes, chevron patterns, triangles, or any other geometric shape you enjoy. Then, spray the areas around the tape, let the paint dry for 1 to 2 hours, and peel back the tape. Try cutting the tape into small squares and triangles and sticking them to the carpet to create your own geometric patterns. It may help to use a measuring tape to map out where you want to place the painter's tape for a symmetrical design. Create a classic border of stripes around the edges of the carpet with lines of painter's tape. Use a measuring tape to measure out where you want the border lines to go, then make small tick marks with a light-colored washable marker. Lay the tape according to the tick marks. The areas covered by tape will reveal the current color of the carpet. Hold up a piece of cardboard at a 45-degree angle next to the tape line to protect the inside section of the carpet from the paint. Blot the painter's tape or stencil with a rag to soak up any puddles of paint that may have collected on them. That way, when you peel away the tape or lift the stencil, the puddle won't drip onto the carpet and ruin your design. Pull up the tape or remove the stencil only after you're finished painting that area. Touch the painted area with your finger to make sure it's dry before moving on with a new color or before laying down more painter's tape. If your design requires adding more tape to previously painted areas, wait until those areas are completely dry. For instance, if you spray red spray paint over blue paint that isn't dry, you could end up with purple areas. Placing tape onto still-damp painted areas will compromise the consistency of the paint and, as a result, mess up your design. Use a paper towel to wipe up as much of the excess paint as possible, then douse a cloth with paint thinner and blot or rub the affected area until you don't see any traces of color. Mineral spirits or acetone can also be used to remove paint. Avoid stepping on the painted areas of the carpet for the next 8 to 10 hours or until it's completely dry. Depending on the climate and humidity of the area you live in, this could take up to 12 or even 24 hours.

Summary:
Use a stencil to create curved, intricate designs. Lay down painter's tape in geometric patterns for a modern look. Apply stripes of painter's tape around the edges of the carpet to make a border. Use a rag to remove any puddled paint on the tape or stencils. Allow the paint to dry before adding a new color or more tape for the design. Use paint thinner to clean up your design or erase mistakes. Wait 8 to 10 hours until the rug is completely dry before walking on it.