Fig. 4From: Novel nannofossils extraction methods from paintings, coupled with GC–MS for provenance determination and binder analysisEvaluation of the interaction between the ultrasonic time and the number of calcareous nannofossils after the treatment. Champagne chalk (CC) was soaked in distilled water during the ultrasonic procedure. The ultrasonic was set for 0’, 10’, 30’, 60’ and 120’s (CC0 to CC120)Back to article page