Realism is the key to a successful fake-blood application, even if the liquid itself looks real. Use several different household items such as eyedroppers, rubber gloves and plastic sandwich bags to create realistic drips, smears and splatters. Test a few different techniques on an old T-shirt or scrap paper to hone your application style before applying it to a friend or a costume.
Fake Wound Enhancement
Give a faux gash or wound a much more fresh appearance with dripping fake blood. Use a large eye dropper or syringe with a wide opening to create blood drips from slices, gashes and punctures with accuracy. Hold the dropper or syringe near the top or midpoint of the fake wound material already on your -- or your friend's -- body; then squirt out some of the fake blood. For a large slice-style wound, run the blood over the entire length or width of the gash. Keep the body's position in mind when applying the blood; in other words, don't apply the blood to a person who is lying down if you want the wound to look as if it happened while they were standing up. You don't want the blood to drip travel in the wrong direction. Thicken homemade fake blood with cornstarch or corn syrup, or thin it with water to make it more runny. Be mindful of potential allergies for the person ready for the faux-blood treatment -- tell him the ingredients and ask about sensitivities up front before applying the substance.
Choose clothing you don't mind sacrificing for the fake-blood treatment -- no matter what the formula, there's a good chance some of the fake blood may stain the outfit. Plot out the blood positions before applying it to clothing. For instance, a chest wound may have a lot of blood emanating from a central spot, while blood on a butcher's apron may involve lots of hand-wiping and random marks and spatters. Apply the blood to the clothing set atop a plastic tarp instead of on someone's body, ideally. For blood emanating from a large wound, soak a sponge or cotton ball in the fake blood, pressing the soaked material into the clothing in the desired location. If you wish for the blood to drip downwards, hold the clothing up while propping it up with your free hand from the back while applying the liquid. For hand marks and general butcher-style markings, wipe faux-blood-coated hands on the fabric, as well as a knife or two dipped into the liquid. Wear rubber gloves and old clothing while applying the blood, as it can get quite messy.
For minor spatters, hang the clothing up on a hanger with a plastic tarp behind the material. Dip a wooden spoon, whisk or even your rubber-gloved hand into the blood, flinging it toward the clothing. Give the same treatment to a person by first having them wear goggles or covering their face completely; extra blood can be added in later. Keep in mind the direction of the splatter based on the back story of the character and situation the blood represents. For large gushing splatters, fill a zippered sandwich bag with an ample amount of fake blood, leaving the bag open. Drop the bag atop the fabric or item you wish to splatter. Keep the entire ground and surrounding area covered with plastic tarps to prevent stains.
Even if the blood is made completely from non-toxic substances such as corn syrup, food coloring and cornstarch, do not apply it close to the eyes or above the eyebrows where it may drip into the eyes. Even the most gentle fake-blood solution can irritate eyes and may be quite difficult to flush out, so it's best to prevent the situation completely.