Rare glass onion bottles restored after 300 years under the sea

Two glass onion bottles that survived 300 years under the waters of Florida’s Atlantic coast have been successfully liberated from marine encrustations and returned to shininess. Conservators at the Florida Division of Historical Resources Bureau of Archaeological Research’s Conservation Lab were able to salvage these rare surviving examples of 17th century glass by cleaning them of thick concretion layers and consolidating the fragile surface.

The bottles were recovered from the wreck site off the coast of Indian River County in 2021 and 2022. The specific ship could not been identified, but it was part of the 1715 Spanish Plate Fleet, the convoy of gold, silver, gemstones, tobacco, chocolate, spices and indigo transported from the New World colonies to Spain. Eleven ships from that fleet were destroyed by a hurricane off the coast of Florida.

Onion bottles were made using the free-blown technique: molten glass inflated by the glassblower through a blowpipe rather than made with a mold. Every piece produced with this technique is unique in shape, size, thickness and weight. They were used in trade for their contents as well as utilitarian objects. On the ship, these bottles likely held an alcoholic beverage drunk by the crew and passengers.

This type of bottle is fragile and rarely survives intact. They were usually broken in the wreck of the ship, and if they did somehow manage to reach the seabed in one piece, they would be constantly subjected to rough treatment by tidal forces. As they were buffeted about, they also crusted up with sand, shells and other assorted marine creatures. Over time, the concretions and constant exposure to sea water would cause the glass surface to delaminate (ie, thin shards of glass flaking off).

It took conservators seven months of painstaking work to clean and stabilize the fragile vessels.

With meticulously slow cleaning and drying, the bottles remained intact and were then consolidated with Paraloid B-72, an acrylic resin based consolidant typically used in glass and ceramic conservation. Several coats of this stabilized the remaining glass flakes that were flying off and gave the bottles that shiny appearance you can see in the after-treatment photos.

The newly-restored onion bottles are now available for exhibition at local museums through the Florida Division of Historical Resources’ Artifact Loan Program.

* This article was originally published here