Inside-out glass

We mostly see glass pipes that have colour patterns on the outside surface of the glass but if you know a really good blowers they could make pipes that have the patterns on the inside. This is usually called as "inside - out" work. All the setout is surely more difficult and time consuming for the blowers but it is really worth it. Products looking like that are very attractive and mind-blowing. How does it work? The entire color pattern is magnified by the thick layer of glass between the outer surface of the glass and the pattern. Also, as the inside work melts flush with the inner surface of the pipe, the color patterns 'sink' into the glass causing beautiful 3 dimensional structures to appear deep inside the glass.