Saturday, July 5, 2014

A Salty Phrygian Trefoil Jug

Posted by William

We started this season at Gordion with a condition survey of the collection on view at the Gordion Museum. This survey of the museum collection occurs on a yearly basis to allow condition comparison with previous years.  This year during our survey a trefoil ceramic jug had developed the presence of salts, a common problem with some archaeological materials.  The ceramic was excavated in 1965 and found in a secondary pit.  It dates to the Middle/Late Phrygian period (7th – 4th century B.C.) and would have likely been used for pouring liquids.  The jug was taken off view and a condition report was recorded and before conservation treatment images were taken.  
Before Treatment

Before Treatment
Before Treatment Interior
Taking Before Images
The desalination of ceramic materials involves removal of soluble salts acquired from archaeological burial conditions, manufacture and use, and previous conservation treatments.  Soluble salts typically appear as white efflorescence on the surface of the ceramic body.  Their removal is necessary for preservation of the ceramic due to their harmful characteristics.The previously restored fill in the ceramic was removed before desalination.  This was done carefully using a scalpel as well as dental picks.  The decision to keep the plaster fill was made as it was in great shape and was not causing damage to the object.  In order to remove the fill safely it was necessary to cut it into two pieces.  Excess plaster on the inside of the vessel was also removed.  After the fill was removed the ceramic was ready for a desalination treatment.  
Removing the Restored Fill
One Section Removed
The general technique for removal of soluble salts involves soaking the object in less contaminated water, so that concentrated salts in the object diffuse out into a less concentrated solution.  In order to carry out the desalination treatment, a source of deionized water is needed. The tap water on site has high conductivity and must be treated to remove minerals prior to use in desalination. This is done using a deionizing column onsite. 

Making Deionized Water
Vessel in Water

To determine the endpoint for desalination an adjusted conductivity measurement (a number representing a conductivity reading adjusted to take into account the ceramic weight and volume of water) is made by entering the data into an equation.  It was determined that soaking the ceramic in deionized water for three days was sufficient for the removal of salts.

Measuring Conductivity of the Water

Entering the Data in the Equation

The ceramic was removed from the desalination bath and allowed to dry overnight.  The edges of the vessel were then cleaned using a dental pick and the restoration paint was removed from the plaster fill.  

After Removal from Deionized Water

Removing Excess Plaster from the Edges

Removing Restoration Paint from Plaster Fill
The plaster fill was reattached by first holding it in place with tape and a padded close pin.  Small bridges of glass microballoons in paraloid b-72 were used to secure the fill to the ceramic and the remaining areas were then filled using microballoons in b-72. 

Reattaching Plaster Fill

After the fill was replaced it was sanded to make a smooth transition between the microballoons and plaster fill.  A small incision was made around the fill to identify it as a restoration and a primer coat of paint was applied.  

After Reattaching Fill
Liquitex acrylic paints were used for inpainting the restoration.  After conservation treatment images were taken and the trefoil jug was then returned to the exhibition case in the Gordion Museum. 

After Treatment Image

After Treatment Image 

After Treatment Image Interior
Phrygian Trefoil Jug Back on View in the Gordion Museum