Complex sentence: Gaucher then returned to the École to study printmaking with Albert Dumouchel, where he created a controversial technique of heavy embossing, which he described as challenging the traditional "taboos".
Split into simpler sentences: Gaucher then returned to the École to study printmaking with Albert Dumouchel, where he created a controversial technique of heavy embossing. When met with criticism, he described his technique as a way of challenging the traditional "taboos".