For the big 3D globe logo the client asked to it to look like concrete or granite. There are plenty of ways to do this but the easiest is with paint. The fellow who is making the globe will most likely have the globe hard coated with a bed liner type spray. This will leave a slightly bumpy texture. The piece can then be painted a solid or blended solid color with as many coats as necessary. In our shop we would most likely use a top quality 100% acrylic house paint and brush it on too. For the rocks on a recent project we painted it just this way. Then came the quick magic step.
To get the different colored dots or speckles we use an undercoat gun with only twenty-five pounds of pressure. Higher pressure will give you smaller dots or speckles. Undercoat guns are very inexpensive and available at any auto parts store. They come in a variety of shapes and sizes, some with special pots. We buy the cheapest ones with just a pipe, trigger and handle. They are easy to use and easy to clean.
The dark color (brown in this case) was done first. The key is to take it easy and do multiple passes. It is far too easy to put on too many and then you would have to start over. I like to spray from at least there feet away to get an even pattern. Have a helper keep the hose you are dragging around from rubbing across the finished work.
I stick the intake pipe into my bucket and spray away…. rinse after the first color and then go on to the next color. Masking takes a whole lot longer than the spraying by far.
-dan