The test is aimed at detect the presence of sulphates (salts in which an atom of Sulphur is bound to 4 atoms of Oxygen) in the rock. How to extract these salts from the rock? How to choose the extraction spots? How to figure out how many sample are needed? These are not trivial questions. Daniele Arena tells us about the approach used during the first tests done in May in San Vito lo Capo.
Looking for sulphates in the rock
The corrosion studies carried out by the UIAA team show trace of Sulphates (alts in which an atom of Sulphur is bound to 4 atoms of Oxygen) on all the A2 stainless steel anchors affette by the pitting phenomenon. Thus the recommended test "looks for sulphates" inside the wall. The sulphates certainly do not abound in the Italian limestones. They may come from small "veins" into the rock; may be deposited on the wall surface due to external causes ( that is deposited by atmospheric agents, or trivially by a smear of chalk). They could be produced by the decomposition of microorganisms. The test is performed by swabbing the surface of the rock. I took a cotton swab soaked in distilled water; then I delicately rubbed it on the rock, patting and tapping to wash up the surface from all that came from the inner by capillarity, and also from all that was deposited from outside, mainly due to the weather. Of course, the purpose of the sampling is to minimise the presence and the effect of all that has been deposited on the surface by external agents (wind, contact with the climber hands or other) and to maximise the presence of those salts that surfaced from within by capillarity.
The sampling protocol
- The sampling area must be (within a narrow tolerance range) a 20x20cm square.
- The salts are taken from the rock dabbing it with 50cc of distilled water
- The sampling should be carried out from areas that do not appear contamined by external agents (especially chalk)
- The operator must wear clean gloves (to not contaminate the sample with the deposits and the microorganism already in his skin)
- The pots in which has to be stored the sample, and the cotton ball with which is carried out the sampling must be clean.
The sampling procedure
- The operator chooses a rock surface deprived as much as possible of external deposits (chalk, soil, lichens)
- He marks with a small incision the vertices of a 20x20 cm square
- He must wear a pair of clean and sterile gloves
- He pour 50cc of distilled water in a clean and sterile container
- He take a cotton clean and sterile ball. Soaks it with a small part of the 50cc of distilled water and use it to tapping and patting the square of rocks (trying not to leak the liquid, but collecting it with te cotton ball)
- Doing so, the white cotton ball gets more and more colourful. When the color of the ball no longer darkens, it means that the operator can no longer collect more from the rock. Therefore the operator must wring it out in a second, sterile and clean, container.
- Then the operator soaks the same cotton ball with some more distilled water and repeats the procedure until exhaustion of the 50cc of water.
- Then the operator close the pot and keep it for the analysis. And moves on to choose another 20x20cm square of rock to take another sample.
- A rock wall can be or less more porous at different points. Thus in some points the operator will collect the 90% of the liquid, and in other points he could collect even the 50%.
- If the sample analysis would not be carried out within 12/24 hours, you must add some disinfectant to the distilled water, to prevent the contamination of the sample due to the products of the decomposition of the microorganisms always present on the rock surface.
- The operator must write down on any container the point were the sample has be taken (the names of the nearby routes, the GPS coordinates, the level on the ground), and shot a photo of the point in which the sample has been taken
- The annotation on the spot, the photos of the area where the sample has been taken must be stored in a database.
Measures: how many and which sample to choose
The veins of sulphate inside of a rock wall are located in specific places. Thus the test results could be positive in some points and negative in other elsewhere.
Choosing the areas in which take the samples, and choosing how many sample must be taken is of crucial importance to obtain significant outcomes. If only one sample gives a positive results (that is contains a percentage of sulphate exceeding the permitted threshold), to say that in that wall there are some veins of sulphate and that the stainless steel anchors cannot be used. On the other hand, though, if all the samples give a negative result, does not completely excludes the presence of sulphate veins in the whole wall. In fact the sulphates could be present in a not examined area.
Thus the operator, in his experience, must carefully choose the areas in which take the samples. He must take a sample for each area in which the rock presents a colour variation (because the colour of the rock depends also from the salt flowering).
Dealing with caves, or with strongly overhanging walls, the oprato must take a sample both in the most sheltered points and in the ones most exposed to the atmospheric agents.
He must discard the areas covered with deposits coming from outside, like chalk, soil, lichens or other.
He must spread the sample so as to investigate all the areas with different colours and morphologies.
An finally, he must remember that even if in all the examined sample the percentage of sulphates doesn't exceed the allowed threshold, he must monitor the state of the anchors, and make some additional test in the points where the breaking of a anchor could cause a serious accident.