After 19 hrs I removed the coral from the tenside, put it on a wire net and let the tenside drip off the fossil over the container. I then rinsed the coral carefully with water and collected the 1st wash-water. Rewoquat in the concentrated form is pretty harmful for the water-environment even though it is biodegradable, so I always collect the 1st wash-water and put it into the hazardous waste collection.

Replace the washing water with fresh water and leave it there for several hours, until no bubbles appear on the surface (1day). After watering the fossil needs to be left to dry completely again before the next round in the tenside. So leave it overnight to dry properly. Repeat the treatment in Rewoquat and water until all clay and marl sediment is removed.

The sediment falling from the fossil during the process of watering can be sieved and examined for micro-fossils.

After the final treatment in the tenside the fossil needs to be watered very well, otherwise remains from the chemical stick to it. I finally put it into the ultrasound bath (with water) for 5 min, where already loosened sediment is falling from the fossil.

Coming back again to the croco-skull: this is a long time project, because the bone being fragile it needs to be consolidated and so from time to time I have to re-consolidate it again. The problem is finding a good consolidant, because water softens it up.

Fig.2: Heliolites sp. before preparation	Fig.3: after 4 treatments in Rewoquat (219 hrs in total)
Click on images for bigger picture

Putting my experiences with Rewoquat finally together I can say that the Pros for the use of Rewoquat are:

• · It is inexpensive (about 5 Euro/ kg) and it can be reused many times. It just gets cloudier and cloudier each time. If there are too many particles in it, replace it with fresh Rewo.
• · It is easy to handle, "preparation while you wait".
• · It can be used on extremely detailed, fragile and very problematic fossils. You get very good results, and it leaves no preparation scratches/ marks.
• · It is very suitable for cleaning micro-fossils.
• · Very good results are received also in combination with other methods, e.g. air-brasive or air-chisels and Rewoquat.

The negative aspects are:

• · There is no knowledge about long-term effects; the article by LIERL was published in 1992 and the author has not seen any changes of the treated fossils since then. (The method was mentioned before that in 1985 (Riegraf) and 1990 (Blank) where it was used successfully both times on microfossils from the posidonien-shale (lowerToarcium); also in combination with other methods, e.g. 1^st treatment with hydrogen peroxide.
• · There are ecological problems even so it is a fabric softener (but highly concentrated): it is forbidden to put any Rewoquat into the water system. It has to go into the hazardous waste collection. Collect the 1^st wash-water as well when using Rewo on a larger scale.
• · Health and safety precautions you have to deal with.
• · So far I could not find a consolidant which is not getting soft in Rewo after 4 treatments (due to the washing water) and so it needs to be put on again. An alternative should be found.