Cobalt-5 is very dense in color concentration, yet not as stiff in workability as Cobalt-6.  Be sure to use a neutral flame with this color as it can be susceptible to over reduction that will leave grey patches or streaks.

Cobalt-5 is great for stringers and blown work that will leave you with a true deep cobalt.   Sandwich between clear layers and blow out thin for a vibrant and beautiful cobalt blue transparent.  Works nicely, and melts easily into itself with no mark or sign of where glass was added.  My favorite Cobalt-5 quality is that it shines through the color when it is brightly back lit.