Materials, cookie sheet, string or wool, cookie cutters and water - and freezing cold weather.
Run 10 inches of yarn through the cookie cutter at the top. Put the cookie cutters on the cookie sheet, placing the ends of the yarn hanging over the edge of the cookie sheet, out of the water. Fill it all with water - maybe 1/4 to 1/2 inch or more depending on the cookie cutters. Don't fill it over the top of the cutters.
For colorful variations, use colored water, add glitter, confetti, or yarn into the water.
Put the cookie sheet outside to freeze. Once it's frozen, run it under water a bit to free the cookie cutters from the sheet of ice. Gently remove the ice shapes from the cookie cutters. Use the yarn to hang your beautiful ornaments outside. Ours are hung street side and in the streetlight at night they really sparkle and light up.