The best method of relaxing specimens is to put them in an atmosphere of acetic acid for at least 6-8 hours. This method is especially suitable for specimens that have been killed using ethyl acetate, but can be used if other killing agents have been used. It is also very useful for softening Critical-point Dried material, as it can prevent breakage when specimens are being card-mounted (if done correctly specimens will not collapse). The best results are achieved using a clear plastic sandwich box with a tightly fitting lid. Cover the bottom with a thick layer of cotton wool. Add a few drops of glacial acetic acid to the cotton wool (about 0.5-0.7ml per 1 litre box). Put specimens on top of a piece of tissue in a glass dish and then place the whole dish in the box which is then closed. With some killing agents specimens may remain stiff after "relaxing". In such instances they can be softened by placing in water for about 10 minutes and then transferring to 70% alcohol. These specimens can then be treated as for air-drying specimens from alcohol (see "Drying specimens from alcohol"). It is also possible to use water or even 70% alcohol in the relaxing box instead of glacial acetic acid (which ought to be used in a fume cupboard or well-ventilated room), but both alternatives may tend to wet specimens so that the wings stick together and the hairs on the thorax may become matted. Use of water or 70% alcohol for softening critical point dried material is not very satisfactory as this increases the risk of specimens collapsing.
Note. It is essential that the correct proportion of acetic acid to box volume is used. Too little and the material will stay brittle, too much and the hairs on the body and wings will become stuck together and matted. It must also be remembered that the acetic acid should be replaced every time the box is used.
Note. It will be found that, if ethyl acetate has been used as the killing agent, material relaxed in the way described above, using acetic acid, will be as pliable as if it has only just been killed.
Last updated 19-Aug-2003 Dr B R Pitkin