The more sand has escaped from the hourglass of our life,
the clearer we should see through it."

   – Jean Paul

Glassblowing is a specialization of the Alchemy skill that allows you to create glass items such as empty bottles, vials, flasks and hourglasses.  You cannot become a glassblower as long as you haven't achieved GM level in Alchemy.  The upside however is that you do not need other 100 points to gain that skill. Fact is, it will not use any points at all so your skill cap will not be affected.  All you need to do, once you're GM alchemist, is to acquire the book on "Crafting Glass with Glassblowing", that can only be found in Gargoyle City in Ilshenar. Your account therefore needs to be at least upgraded for LBR or more recent expansions. The Gargoyle Shopkeepers sell the books for a little over 10k in Gargoyle City, so expect to pay a bit more than that in 2D lands.

To craft your glass items, you will need sand and a blow pipe.  The pipe can also only be bought from Gargoyle vendors in Ilshenar but the sand can be mined at any beach or sandy area in the Old or New Lands.  In order to make items, stand next to a forge, double-click your pipe and select the item you wish to craft.  You will need to have the right amount of sand in your backpack or you will get a message indicating you do not have sufficient resources.  The sand does not stack so you want to have as little items in your pack as possible to carry more sand.
 
The full set is comprised of 26 items. In order to obtain the other colors, have the items face different direction or activate the spin on the hourglass, lock down the item in your house and use your interior decorator on it (turn option).

Keep in mind that the blow pipes will wear out like any other crafting tool.  So you will need to always have a few of them handy.