The year is 1568. A man in Venice, Italy, stands over a scorching wood fire. He is making glass. He doesn’t have fancy tools—only a long blow-pipe and some tongs. He can’t flick on an electric switch for better light. The lightbulb hasn’t been invented yet! Instead, he relies on daylight and the glow from his fire to see. His glass will be sold to kings and queens. But his glass-making method is top-secret. If he tells anyone how he does it, it could cost him his life!

Venetian glassmakers like this one hid their techniques for hundreds of years. But now a modern-day glassblower may finally have discovered their secrets. William Gudenrath started blowing glass when he was just 11 years old. As a teenager, he started to wonder about Venetian glass. How was it really made? He looked for information about it. But he could find barely anything. The Venetians were such good secret-keepers that it seemed like nothing had even been written down about how they made their glass.

Today, Mr. Gudenrath works as a glassblower and researcher at the Corning Museum of Glass in Corning, New York. Mr. Gudenrath has studied Venetian glass for decades. But studying it wasn’t as simple as pulling out a book and looking for “V” for “Venetian glass.” He had to try copying old Venetian glass himself. Old Venetian glass is very clear, thin, and light. That kind of glass is difficult to make. It was very difficult hundreds of years ago. People back then couldn’t just crank a knob on an electric oven to adjust its temperature. That meant they had to do perfect work—fast.

Mr. Gudenrath also had to take many trips to Italy. There, he looked at glass made in Venice today. Mr. Gudenrath published his findings on the Internet. Now anyone can watch videos of Mr. Gudenrath making glass the way he thinks Venetians once did.