372 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Until a few years ago there were many varied types of sizes of caps and threads used, but this variety is being reduced although it is still extensive. At present the bulk of closure finishes come within the British Standard 1918, in which there are two specified types: shallow continuous thread finishes and tall continuous thread finishes. There are no dimensions specified in B.S. 1918 for screw cap, whether metal or plastic, but a method of testing caps with gauges is laid down. This is, in short, that screw caps, whether metal or plastic made to fit British Standard R-3/2 and R.4 glass finishes, shall be gauged by the use of a double-ended gauge, each end of this gauge being of certain maximum and minimum glass finish tolerances. The caps shall fit both ends of gauge. The overall diameter dimensions of shallow finishes range from 0'694 in. to 4.704 in., and that for tall finishes from 0'506 in. to 1.193 in. this is a wide range that includes sizes suitable for practically any purpose. There is one other feature regarding the weight of caps that is worth mentioning since with the modern trend of industry more and more caps are required to suit automatic assembly conditions. Generally speaking, caps used for automatic assembly on bottles have to be more robust than caps used for hand assembly, and resulting from the use of more material to make a robust cap it is common for caps used in automatic assembly to be more expensive than lightweight caps. To sum up for moulded caps, indications are that their overall use in various bottling trades is still increasing, and it would appear unlikely to decrease in the foreseeable future. METAL SCREW-ON CAP There are two types that are in common use: one that is completely prefabricated before use and the other prefabricated in a cup form. When used, this second type is placed upon a threaded bottle neck and mechanically rolled so that the shape of the container thread is formed on the cap. Metal caps are made from decorated pure aluminium, aluminium man- ganese alloy, tinplate, or blackplate this latter is essentially rolled steel plate of the same type that is used in the manufacture of tinplate, thick- nesses of material used being in the region of 0-009 in. to 0.020 in. Decoration is invariably done before fabrication and is in the form of coating, printing and varnishing also in a few instances, embossing. There are no definite laid down dimensional standards for metal caps in Great Britain. In practice there are mainly two types: those that agree with the rolled-on closure finishes, and those that agree with the B.S. 1918 closure finishes, the latter in turn being composed of two types, R3/2 and R.4. The laid down method of checking caps to fit these finishes is the same as that for moulded caps. Liner materials used in metal caps usually are of the same type as those

BOTTLE CLOSURES 373 used in moulded caps. In addition a rubber latex or polyvinyl acetate base compound can be flowed into caps and set with heat treatment. A difference in the retention of liners is that the majority of metal cap liners are friction fitted into a recess, whereas the bulk of moulded cap liners are glued in. Some advantages and disadvantages of the use of metal caps are: 1. With correct dimensions of cap and container, suitable cap liner and good application, satisfactory use can always be expected. 2. They are virtually unbreakable. 3. There is a slight price advantage over moulded caps. 4. Metal screw caps do not have the same sales appeal as plastic caps. ' 5. Frequently they appear to be affixed to containers too tightly also, if dented when on bottles, caps can be extremely difficult to remove 6. To avoid corrosion of metal some care should be taken in storage. METAL SPRING OR CLIP-ON CAPS There are many types that come under this heading. Some that are widely used are: 1. Decmated tinplate lever caps that are used for gin and whisky bottling where a tin-wrapped composition cork liner is used. This type o! closure can be re-used with safety, and has had some popularity in the British spirit bottling trade for some years. 2. The aluminium cap or seal used for the bottling of preserves which have a liner ring of flowed-in rubber or polyvinyl based material. In many instances the caps are used for purposes where they are sterilised. These caps can be decorated by coating or printing to any requirement in all cases a sanitary lacquer is applied to inside surface. In use, the pre-formed caps are crimped on to jars or bottles in much the same manner as crowns. With sterilised containers a vacuum is invariably created which has to be broken by perforation or leverage before cap can be removed. This type of closure has had increasing popularity for the last ten years. No doubt this is because of its efficiency and the fact that it can be used on common jam jar finishes. 3. Phoenix Seal. This is the conventional simple tinplate cap with rubber ring liner and separate formed tinplate scaling ring that is generally used on meat or fish-paste spreads. Criticisms of this might be made on account of possible difficulty in removal of seal and cap it is also comparatively expen- sive. However, this type of cap has been used with apparent satisfaction for some time. 4. Metal Press-on Caps. Liners used in these are usually of the ceresine faced wood pulp or composition cork type. This closure is fairly economical