The key challenge of the experiment was addressed: our ability to achieve the required level of radiopurity. Not only had such a radiopurity condition never been reached before, but no detector capable of measuring radiopurity at that level existed at the time. Consequently, in addition to developing methods and facilities to achieve the design radiopurity, we also built a detector, which we named the Counting Test Facility (CTF), to measure the levels of radiopurity attained. After various tests and resolved issues, the CTF demonstrated that we were capable of achieving the required radiopurity. This result earned us the approval of the full-scale experiment, Borexino, by the INFN, along with the associated funding and a funding from the German agencies and later from the US National Science Foundation. The CTF also served as a benchmark for Borexino, allowing us to test certain aspects of the experiment’s design.