With thanks to Red House Crafts, Okra Glass and Royal Brierley Crystal for their help in compiling these tips.
These tips for identifying glass are only a guide and that there are always exceptions to the rules!
Old glass is not normally marked but it is always worth checking the base just in case.
Glass marks can be difficult to spot so always examine the object in good light. Makers' marks were often 'acid badges', a form of branding. Engraved glass is sometimes signed by the artist, but the signature is usually very small and can form part of the design.
Registration numbers are common on glass from the mid 19th century onwards. A diamond mark was used to register early designs then replaced with Rd numbers.
Old glass will usually have signs of wear and tear, particularly on the base. Gilded decoration will also be worn by years of handling.
Pressed glass will usually have seams along the body, often three or four, where the mould opened to release the glass.
A slightly rough round mark on the base is called the pontil mark. It is the result of the hand-blowing process and is sometimes polished down. A rough pontil mark does not necessarily indicate an old piece as many modern studio pieces also have them.
A piece of glass with a pontil mark and seams along the body was probably mould-blown i.e. hand-blown into a mould.
The stopper of a decanter should fit neatly and tightly into the neck of the decanter without sinking below the rim or sticking up above it. If the decanter is cut or engraved and some of the same decorative motifs appear on the stopper, then that is a good sign. The stopper should be the same colour and in proportion to the rest of the decanter. Old glass usually has some sort of tint, whereas modern glass is much brighter and whiter.
To be sure that the stopper for your decanter or perfume bottle is the original, check both the bottle and stopper for a number. In the 19th and 20th century a small number was frequently scratched onto the neck of the decanter and the peg of the stopper. Matching numbers are a good sign that the stopper and the decanter belong together. The numbers are usually single digit, but two and even three digit numbers are known.
To date screw-top perfume bottles, check the lining of the lid - if it is made from cork, rubber or silver, it is pre-1960s. If the lining is plastic, it was made later than this date.
If your decanter does not have a stopper, run your finger inside the neck. If it is very smooth then it is unlikely the decanter was meant to have a stopper, but if it has a matt texture it probably did.
Most factories kept pattern books and registered their designs. The Design Registers for glass are kept by The National Archives. The Museum Service holds pattern books from several factories, which can be consulted by appointment, see details here.
The Millers Collectors' Guides are handy guides on various topics including paperweights, perfume bottles, glass of the 20s and 30s, glass of the 50s and 60s, and popular 19th and 20th century glass. Shire Publications publish a series of pocket-guides on glass topics, including English drinking glasses 1675-1825, bottles and bottle collections, Carnival glass, pressed flint glass and studio glass.
Other reference books are available that identify makers' marks and help to identify and classify glass. The following provide comprehensive lists of pressed glass registration numbers.
Millers "Collecting Glass: the facts at your fingertips" is a general guide to styles and techniques with useful tips on collecting glass.
"The Identification of English Pressed Glass: 1842 - 1908" by Jenny Thompson
"Registration Numbers 1908 - 1945" by The Glass Association
For serious glass collectors the two volumed "Glasmarken Lexicon" is the most comprehensive guide available covering makers' marks, signatures and badges.
Please note our glass opinion service is closed due to limited staff resources. If you require assistance with identifying your glass, you may want to consider contacting an auction house, see the list below, the Glass Association or the Glass Message forum for further advice.
The Museum Service is unable to provide valuations or consider insurance claims as this goes against professional codes of practice. A reputable auction house may be able to help you. The following is a list of well-known auctioneers, but we are not responsible for any response you receive.
Walton & Hipkiss, tel: 01562 886688