Clara was born in 1921 in the small village of Rolde, Province of Drente, in the Netherlands. Her family situation was unusual for that time and place, as her father was a divorced, remarried minister of the Dutch Reformed Church. She had two half brothers from her father's first marriage to a minister's daughter whose brothers were also ministers and were strongly opposed to their sister's divorce. Clara's mother was much younger than her father and was relatively uneducated, not having completed high school, but both Clara and her sister, who was two years older, were expected to be educated to the same level as their two half-brothers. She believes her father felt that it was only fair for the daughters to have all the same advantages that the boys had. He was quite liberal in his theology and in his views about the advancement of women, and he expected his daughters to go to the university when they completed high school.

Although Clara moved a number of times during her childhood, presumably due to her father's employment decisions, she remembers that school was interesting, especially science and math which were not subjects that seemed overly difficult or formidable to her. She and her sister traveled by train, and later by bus, to another town to attend high school doing some of their homework during the long ride to and from school. Her sister preceded her to the university majoring in biology. Her father did not have the financial means to pay the costs of both daughters attending college, so fortunately for Clara she was awarded a much-coveted interest- free government loan, based on merit and need, to help pay for her college education. When she arrived at the University of Leiden in 1938 she declared a major in chemistry with a minor in physics. Six of the 20 students who were declared chemistry majors in her class were women. Only one of them, besides Clara, continued through to completion of her degree, and she became a high-school teacher. The others, later in life, practiced chemistry at an assistant level.

Although the winds of war were blowing across Europe in the late 1930's, Dutch universities were not generally affected until Clara was already into her graduate studies. The Germans occupied Holland in 1940, but initially left the universities alone. However, in 1941 the Germans dismissed all the Jewish professors at the universities throughout Holland. A young professor in Leiden spoke out against the dismissals and prompted a student strike that resulted in the Nazis immediately closing Leiden University until the war ended. Clara was allowed to take her exams and complete her Candidate's degree before she left.

The University at Utrecht was still open, so Clara continued her work there toward her Doctoral degree until the Germans required the signing of a loyalty oath by university students in 1943. From then on work at all universities (except at Leiden University which remained closed) continued on a much reduced scale. At that point Clara moved back home with her parents near Leiden while she commuted and worked for a professor at Delft. During this time she was able to continue her studies at home and take small exams, when she felt she was ready, through personal contacts with professors in their homes. In this way she was qualified to take the final examination and receive her Doctoral degree in 1946 when the university opened again after the war. Her practical work had been completed in Utrecht and her course work during her years of studying at home.

Her major professor for the Ph.D. degree was Anton Eduard van Arkel, who had been her professor since she came to Leiden as an undergraduate. A.E. van Arkel was a noted Dutch inorganic chemist who developed the theory of the chemical bond in inorganic chemistry based on the electrostatic interaction between ions. He was recently cited as the author of the "bond- type triangle", a diagram that represented the progressive transition between the three extreme cases of pure ionic, pure covalent, and pure metallic bonding.(5) Clara had always found van Arkel very supportive of women in science and she recalls that he had a number of women on his staff. This no doubt contributed to the fact that 30% of the declared chemistry majors in 1938 at Leiden University were women.

In 1946 van Arkel personally encouraged Clara to take up the study of X-ray crystallography, so that she could become his assistant. Dr. Ketelaar, who had been running the X-ray crystallography laboratory at Leiden, had recently left, and van Arkel asked Clara to take over his work. Van Arkel arranged for Clara to receive training in Amsterdam with Caroline MacGillavry, a highly skilled and recognized expert in the field of X-ray crystallography. Thus Clara continued her graduate studies working one day each week with MacGillavry in Amsterdam and the rest of the week working at the University of Leiden. According to Clara MacGillavry was a wonderful person with whom to work. MacGillavry was clearly a major influence on Clara's favorable introduction to this discipline. Although MacGillavry was employed as a reader at Amsterdam University at that time, eventually her work was so distinguished that a professorial position was created for her. She was active in the international world of X-ray crystallography and had many contacts in other countries.