The people of the ancient world very likely discovered ways to make glass accidentally while firing what is called Faience, which is a kind of pottery that is glazed with a sodium compound. If the glaze mixed with the clay prior to firing, the result would be a glassy substanced created in the clays body. 

Making glass had its origins in the Palestinian area, and was further developed in Egyptian areas around 1500 BC. 
The Phoenicians worked with the glass and became the greatest of all the glass makers in the world of ancient times, probably because of the abundant natural resources(silica sand) that glass making required which were found in their area. 

Glass was not plentiful as it is today. It was used in much the same way and was thought of in the same way that semi precious stones were and in fact, held the same status as they did, being nearly as rare. 
Decorative glass was quite  rare, and was difficult to produce, since it was in its infancy so far as an art form, so it was used in place of precious stones in many cases, to decorate jewelry, in decorative pots and jars and to make figurines or add color to them . 

Glass vessels made in ancient times were created using molds, and the earliest example of this molded type glass was found in a tomb, that of Thutmose’s three foreign wives, which offered up a glass vessel that had been molded as well as many beads and two more unusual type vessels also made of glass. This leads to the speculation that glasmaking probably came to Egypt during Thutmose III reign. 

The glass made in ancient times was, or so its said, made from sand quartz. Other chemicals were added to lower the melting point, so in effect, the ancients were using some very complex chemistry to both creat the glass, as well as to color it. 

The impurities that were contained in ancient glass are what gave it its color, with maganese adding the pinks and violets, while sulfurs gave them the greens and yellows and various types of things such as azurite, added on purpose after a time, created lovely deep blues. 

Imagine that experimentation and the trial and error that were necessary in such times. 

Glassblowing itself didn’t really take place until about 50 Bc, reportedly near Palestine, which is believed since the first blown glass we found was found near Jerusalem. 

Prior to that time, only the very wealthiest could afford glass of any kind, but with the advent of glass blowing, it was possible to make a lot of containers and to do it far more cheaply so that more people could actually afford and avail themselves of glassware products.