Ancient Glass Blog of The Allaire Collection


Posted in Uncategorized by Allaire Collection of Glass on June 1, 2021

113E Facon de Venise Wine Glass in The Allaire Collection

Date: 1700 c. Height: 11.5 cm Weight: 47.5 g

Description: This delicate wine is from Northern France or Southern Netherlands and is made in the Venetian style of glassmaking. The vessel has a pointed round funnel bowl with a stem of one flattened solid knop and solid base knop attached to a foot. The foot is funnel-shaped with a turned under edge. A faint purple tint can be seen throughout this diminutive glass.

Remark: The faint purple tint of this initially colorless wine is the result of being exposed to sun light and it’s UV radiation.  A similar color change can be seen on clear colorless glass doorknobs made before 1900 which have a light purple color.  To understand why this happens you have to know something about the chemistry of ancient Roman and Venetian glass. This active link is to Chemistry on Roman Glass.  The glass makers at the time this vessel was made used manganese dioxide to decolorize the glass of its natural pale green color.  The pale green color was caused by the impurity of iron oxide in the raw materials used to make the glass.  So, what happens when a decolorized glass object is exposed to direct sun light over long time? It is generally accepted that the ultra-violet light initiates an electron exchange between the manganese and iron ions. This photochemical phenomenon changes the manganese and iron compound into a form that causes the glass to turn a faint purple.


One Response

Subscribe to comments with RSS.

  1. wynkin said, on June 1, 2021 at 6:32 am

    In the dark, illuminated with UV the effect is even more obvious.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: