The simple spot tests are a great assistance in separating superficially similar species in the field. A newcomer to lichenology often finds these tests indispensable as they struggle to identify specimens. Government regulations and a general tightening of safety standards make it almost impossible to obtain some of the necessary reagents. There are three commonly used tests: K (Potassium hydroxide), C (Chlorine), Pd (para-phenylenediamine. In addition, you may need to use hydrochloric acid, nitric acid, or iodine. These notes provide cautions on their use and some acceptable substitutes. Immediately, wash any spills with water, preferably running water.
K
Many keys depend on the spot reactions given by potassium hydroxide (K). An easily obtained alternative for this chemical is therefore needed. A good substitute may be found in a solution of caustic soda (sodium hydroxide). Caustic soda powder may be purchased at any DIY store and a solution should be made up with water. The strength is not critical but about 10% caustic soda to 90% water by volume should work well. If too strong a solution is made the reaction is very slow and it is difficult to get it to wet the lichen tissue. The solution should be tested on Xanthoria or an orange Caloplaca, if there is an almost instant crimson reaction, the strength is suitable. As it is caustic, strictly follow the warnings on the bottle and observe the usual precautions to prevent it getting on the skin, in the eyes, mouth etc.
C
Sodium hypochlorite (C) presents no problem as it is found in most domestic bleaches. Recently, some 'new and improved' thick bleaches have become popular. These contain additional substances to enhance the bleaching effect. Unfortunately, some of these additional substances contain potassium or sodium ions which can give false colour reactions in the test. It is recommended that you use the unimproved liquid bleach. These are still generally available as the lower cost generic version of bleach. Before using a commercial source of bleach, it is recommended that you test it on the medulla of Parmelia sulcata or P. saxatilis. If you do not get a C- result use another bleach.
Pd
The use of para-phenylenediamine (Pd) is probably best avoided in the early stages of lichenology due to its possible health risks.
Over the past few years there has been much discussion amongst lichenologists concerning the dangers inherent in the use of para-Phenylenediamine. It is known to be carcinogenic but recent evidence seemed to suggest that the dangers were remote and that it was only a very weak carcinogen.
However, the latest work on this compound indicates that it should be treated by lichenologists with great care. Articles in The Times (January 6 and 22) and the British Journal of Dermatology emphasise the inherent dangers of para-Phenylenediamine. An especial danger is present in its easy absorption through the skin. A study in the United States found that people who used this, or similar products, as permanent hair dye can treble their risk of bladder cancer. A survey reported in the British Journal of Dermatology of 612 people suffering from eczema, gave a result whereby 4.2% of them developed contact dermatitis of the scalp after using para-Phenylenediamine as a hair dye. A woman in Birmingham recently died from anaphylactic shock after her hair was dyed using a mixture that contained para-Phenylenediamine. However, there is no other record of a similar death in the literature and one cannot therefore be certain that this substance was the cause.
Other cases do have a direct link to para-Phenylenediamine. For instance, it is a custom in the Middle and Far East to produce intricate patterns on the hands and face using henna. The henna dyes the skin and the patterns remain visible for some weeks forming a temporary tattoo. Tourists to these areas often pay to have such temporary tattoos painted on their skin. Genuine henna is a rather expensive substance and unscrupulous artists have substituted para-Phenylenediamine as it is considerably cheaper to purchase. A seven year-old girl from Newcastle was on holiday on Greece where she had such a temporary tattoo of a four inch long dolphin painted on her upper arm. Her arm swelled up and developed large blisters. She also found that subsequent exposure to sunlight caused her to come out in a rash. Dr Aileen Taylor, the consultant dermatologist that she saw on her return, stated that this was the fourth case that she had seen in a year. She said that this patient was sensitised to para-Phenylenediamine and would have to be careful about exposure to sunlight for two years and probably would never be able to wear make up. Dr Celia Moss, a consultant dermatologist at Birmingham Children's Hospital, stated that she had seen numerous children who had had allergic reactions to dyes that contained para-Phenylenediamine.
With its simple passage through the skin, these and other cases suggest that great care should be used when working with para-Phenylenediamine. Even when extreme care is taken in removing a crystal from a bottle, minute brown stains from this chemical will often appear at a later date on the paper where the test was carried out, demonstrating how easily it can be spread. Especial care must be taken when dissolving it in alcohol. The alcohol rapidly evaporates and leaves a fine deposit that can easily be blown about and then breathed into the lungs.
A. W. Archer (The Bulletin No. 60 Summer 1987) mentions Santesson's idea of using o-dianisidine but this is also thought be a carcinogen. He suggests using the photographic developer known as 'Colour Developer 4' in a solution with anhydrous sodium sulphite. The article includes a list of the colour reactions given by this solution compared with those produced by para-Phenylenediamine. Further work is required on substitutes for para-Phenylenediamine but until then, do not let your interest in lichenology be the death of you.
HCl
For the beginner in lichenology, another problem with keys, is that they often have to decide whether a stone is siliceous or calcareous. The two standard methods are to use dilute hydrochloric acid to see if it fizzes. If it does it can then be considered calcareous. Alternatively, it may be assumed to be calcareous if it has orange, crustose, K+ crimson species. A rather circular argument if you cannot yet identify any lichens.
Acids are also now difficult to purchase but kettle descalers (available at a DIY store) are a good substitute though you may need to dilute the acid somewhat. Take care when using descalers as the acid is strong and the fumes can be dangerous. Lemon juice, as purchased in a plastic lemon, is another alternative. This gives fewer bubbles than in the reaction with hydrochloric acid but sufficient should be seen to give an identification. The reaction is more easily observed if the drop of lemon juice is examined under a hand lens. Vinegar may also be used, but this gives a weaker reaction and usually only works on dry stone. Any dampness causes the vinegar to spread out and become so dilute that no reaction takes place. This does not happen with HCl or a lemon squeezer, unless the rock is running with water they remain as a drop and the fizzing can be seen.
Nitric acid
Nitric acid can be used to distinguish between Melanelia and Neofuscelia. Unfortunately, there is not readily available substitute.
Nitric acid is not easily obtained. It is best used in a laboratory in a fume hood. Do not carry it around in the field.
I
Some tests require the use of iodine. Tincture of iodine cannot be used but for sensitive microscopic work this solution is too strong but it can be used in field tests that call for the iodine test. For critical microscopic work, you will need to prepare the solution according to the prescription.