We were recently traveling overseas and visited a desert and some beaches. As the result, we now have a small collection of interesting looking shells and rocks. Now that we are remodeling our kitchen, we had an idea of somehow incorporating them into the backsplash. The attached photo shows mostly the rocks. I have no idea what type they are (sedimentary/volcanic/etc). The main question is: given their odd shape and varying size (e.g. the one at the bottom of the photo is about 3" X 2.5"), is there any way to attach them securely to the wall? Do we need to use some special type of adhesive? Do we need to prepare the rocks and shells in any way, e.g. clean them in a special way, polish them etc? Once installed, is there any way to make cleaning them, and the backsplash areas around them, easier?