As a fluid artist, I enjoy making coasters because they are all unique and a great gift for anyone. I seal them with resin so they are durable with cold or hot drinks. People love the coasters because not only are they beautiful, but they are unique. These coasters are resin art on acrylic with a cork backing. They are 4". I still make them a lot as I continue to work on more advanced techniques. They are like little pieces of art and they are all unique. Please keep in mind that no resin coat will be absolutely perfect. We cover them, but can't entirely avoid an occasional speck of dust.