Your Glass

• Do not stack tumblers inside one another as this can cause stress cracks and tumblers can get stuck.
• Wash crystal in warm soapy water and dry with a soft cloth. Never wash your crystal in the dishwasher as the cleaning agents are abrasive.
• Very hot or very cold water can cause sudden stresses to glass, particularly where the glass is thick.
• When draining avoid placing glasses upside down as this can put a strain on the rim.
• Water should not be allowed to stand for too long in vases since the acids in flower stems can, over a period of time, etch the surface.
• To clean your glass, a light dusting should be sufficient. Use a soft-headed toothbrush for awkward nooks and crannies, providing the glass is not enamelled or gilded.
• If your glass requires washing, use warm soapy liquid - mild washing-up liquid is fine - in a plastic bowl to protect the glass from the hardness of the sink. Dry with a soft, clean lint-free cloth.
• If the glass is iridised, the piece should be dried immediately as watermarks can appear on the shiny surface. If this happens, simply immerse in water then dry.
• If the glass has sand-blasted or acid-etched decoration, clean the piece as above, then pour a little oil - baby oil or cooking oil will do - onto a piece of lint-free cloth and rub onto the surface. Remove any excess oil then polish with a clean, dry lint-free cloth.
• Avoid bumping pieces together, such as paperweights, as this can cause bruising or fracture marks.
• Beware of handing glass when wearing diamond rings - diamonds can easily mark the surface of glass.
• When transporting glass, always make sure it is well wrapped, ideally in a generous layer of tissue paper then a layer of bubble-wrap. When packing boxes, stuff any gaps with tissue or newspaper so the glass cannot move. Make sure the box is sturdy enough to hold the glass and do not overfill boxes - you might damage yourself as well as the glass by making boxes too heavy.
• When packing decanters or perfume bottles, always remove the stopper and wrap it separately.
• Create cushions of tissue to support fragile stems, points or awkward parts so the weight of the glass rests evenly when it is laid flat.
• Items made from coloured glass, rather than colours applied to the glass cold, will not fade so do not be afraid to display them on a windowsill. However, beware of displaying paperweights on a wooden windowsill or table close to direct sunlight as the thickness of the glass can magnify the sun's rays and scorch the wood.

• If the decanter is old (pre 1930) and the inside is badly lime-scaled, then the only way it can be effectively cleaned is by mechanical polishing - this should be done by an expert restorer. Lead shot is put inside the decanter together with jeweller’s rouge and water and the decanter is then stopped up with a cork. The decanter is wrapped in bubble wrap and then placed inside a revolving tumbling machine for a couple of days.
• If the decanter is relatively new (post 1930) and is made from lead crystal or full lead crystal, then it can be acid dipped in a hydrofluoric and sulphuric acid mixture. Acid polishing should not be attempted on old glass as the lead content is unpredictable and the decanter could be spoiled in the process. This technique should be done by an expert restorer.
• Probably the best DIY method is to use dishwashing tablets, as they have a caustic effect. However, we cannot be held responsible for the results!

• Put it in an airing cupboard, preferably upside down.
• Roll up some kitchen roll paper and stuff it inside. This should absorb the moisture.
• Use a hair dryer, but make sure it is not too hot!
• Put some alcohol inside (something like Gin), swill it around and then leave to evaporate.

• Hold the decanter between your knees with the stopper away from you and tap the stopper gently but repeatedly with a piece of wood (the back of an old fashioned shoe brush is ideal). The slight shock should release the stopper.
• Wrap a piece of hot wet cloth round the neck of the decanter. The theory is that this will cause the glass to expand and thus release the stopper.
• Warning - the most common cause of stuck stoppers is Sherry as it can be sticky and sugary, so make sure that decanters with Sherry in are kept clean.

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.

West Midlands

• Bonhams (Solihull)

• Fieldings Auctioneers,

• Walton & Hipkiss, Tel: 01562 886688

London

• Christie's

• Sotheby's