FOLLOW THESE STEPS FOR OPTIMAL RESULTS:
Preferably choose a light color Powertex such as Ivory, Yellow Ocher, Terracotta or Red. Cover the object completely with a layer of Powertex of your choice and let dry. Make meanwhile in a cup, a spatulable paste by stirring Powertex + a pinch of 3D Sand, and 10 to 25% Rusty Powder to a mouse gray color. Add a few drops of kitchen vinegar and a splash of water. Mix all of this. Apply a layer of this paste with a brush or palette knife on the object to be decorated. For different color effects, you can also sprinkle a little of the powder into the still wet paste and rub it in. The more Rusty Powder you add, the darker the result. Also, the more vinegar, the darker the result. Fill a spray bottle with water and maximum 50% vinegar. Regularly moisten the object with it. (More vinegar gives a faster and darker rust effect). Let it dry overnight. The full result is visible the next morning.