How to Recognise Hand-Blown and Moulded Antique Glass
The way glass was formed can help identify and date an object, but no single bubble, seam or pontil mark proves great age. Examine manufacture evidence alongside shape, colour, wear, decoration and provenance.
Look for mould seams
Pressed and mould-blown glass can show seams where mould sections met. Follow a seam from the base toward the rim. Its height and finish may relate to the manufacturing process.
Seams can be polished away, concealed by cutting or faint on well-made glass. Their absence does not prove free blowing.
Examine the base
A pontil mark may remain where a pontil rod supported the object during finishing. It can be rough, snapped, ground or polished. Some modern handmade glass also has pontil evidence, so it indicates a process rather than an automatic date.
Moulded bases may show pattern detail, registration features or seams. Wear should be consistent with how the object stands and has been used.
Study symmetry and repetition
Free-blown glass often has subtle asymmetry, tool variation and changes in wall thickness. Moulded glass can repeat identical relief detail. Skilled production can make either method very regular.
Bubbles and striations occur in old and modern glass. Their shape and distribution are supporting clues only.
Inspect the rim
A fire-polished, folded, cut or ground rim can reveal how the vessel was finished. Look for later grinding that may have removed a damaged rim and changed the proportions.
Protect the object
Support glass from beneath and avoid tapping it. Do not use scratches, hot needles or other destructive tests. The [Canadian Conservation Institute](https://www.canada.ca/en/conservation-institute/services/preventive-conservation/guidelines-collections/ceramics-glass-preventive-conservation.html) stresses that handling and cleaning are high-risk moments for glass.
Build a complete identification
Compare the object with documented examples of the suspected factory, region and period. Consider decoration, foot construction, colour, weight, tool marks and provenance. Seek specialist advice when attribution materially affects value.
For practical restoration work and close-up workshop discoveries, [watch and subscribe to Antique Repair Shop on YouTube](https://www.youtube.com/@AntiqueRepairShop).
Sources and further reading
- [Canadian Conservation Institute: Caring for ceramic and glass objects](https://www.canada.ca/en/conservation-institute/services/preventive-conservation/guidelines-collections/ceramics-glass-preventive-conservation.html)
- [Corning Museum of Glass: Glassmaking techniques](https://glassmaking.cmog.org/)