How to work with tensides/surfactants:
The tenside used is called Rewoquat W 3690 PG, which is a concentrate of 75% cationic tenside with 24% propylenglycol. It is used for the production of softeners. It has a pH-value between 4.0-5.5. It can disperse with water. Tensides work very well on harder sedimentary rocks with clayish or marly components.
Very often fossils are covered with hard encrustations of marl and clay, esp. corals, brachiopods and crinoids. The usual way to remove such crusts is by the use of the airbrasive, which also easily removes details. Tensides work very well for cleaning, especially on microfossils.

What kind of equipment do I need?
Working with Rewoquat should only be done in a well-ventilated area, if possible in a fume-cupboard; it has a characteristic smell and it can also irritate the eyes. Well-fitting goggles are a must! Rewoquat contains substances which are irritants (Xi R36/38) and degrease skin. Therefore gloves need to be worn whenever handling it. Due to it having 24% alcohol it is flammable and should be stored and handled like any other flammable liquid. Using an air-tight container (eg. Stewart box) prevents any alcohol evaporating. Also needed is a bowl for watering the fossil later on and a brush for removing loosened sediment.

In practice:
The coral I worked on (a heliolites sp. from Gotland) was covered thickly in clay and marl. So to begin with I gave it a careful scrub in water and left it to dry afterwards. The scrub already removed quite a bit of the sediment, but the fossil still covered with a fine layer.

The fossils needs to be dry before putting it into the tenside, otherwise the chemical can not work properly. I then put the coral into a polypropylene box with a well-fitting lid and filled the box with so much Rewoquat until the coral was completely covered.

The fossil is left in Rewoquat for at least 12 hours, because the tenside needs some time to work properly. After 12 hrs you should have a good look, how well it works and how the state of the fossil is. With delicate specimen it is better to take them out after 12hrs and treat them for another 12 hrs rather then leaving them in Rewoquat for too long.