Utrecht University and UMC Utrecht give a mural to the city

Mural Caroline Bleeker in the Strosteeg

De muurschildering van natuurkundige Caroline Bleeker in de Utrechtse Strosteeg.
Photographer Robert Oosterbroek, mural De Strakke Hand, part of Utrechtse Muurformules

A mural of physicist Dr. Bleeker decorates the Utrecht Strosteeg as of this week. UMC Utrecht and Utrecht University give the mural to the city of Utrecht for the occasion of 385 years of science in Utrecht. The painters collective De Strakke Hand realised the mural, which is a part of the Utrechtse Muurformules.

Dr. Bleeker

Caroline Bleeker (1897 – 1985) obtained her PhD cum laude as a physicist at Utrecht University in 1928. Less than two years later, she was the founder of the Physisch Adviesbureau on the Korte Nieuwstraat 13 in Utrecht - within a stone's throw of the Strosteeg – from where she provided information on scientific instruments. In the same year, Bleeker opened an instruments factory in Utrecht. Her successful company produced scientific instruments and later also gained a department for optical equipment. During World War II, Caroline Bleeker hid Jewish people in her factory. She received a royal decoration for this.


After World War II, Caroline Bleeker opened an optics factory on the Thorbeckelaan in Zeist, together with her life partner Gerard Willemse. The name of the factory was NEDOPTIFA: Nederlandsche Optiek- en Instrumentenfabriek.

NEDOPTIFA was nationally and internationally famous for the high quality of its instruments. It was the first company in the world to produce phase-contrast microscopes: microscopes that make it possible to see the internal structures of living cells. The production of these microscopes made NEDOPTIFA a successful company.

Professor Frits Zernike developed the phase-contrast microscope, for which he received a Nobel Prize in 1953. NEDOPTIFA marketed the instrument. In 1947, Caroline Bleeker and Frits Zernike obtained the patent on the phase-contrast microscope.

Phase contrast

The phase-contrast technique is still used in hospitals, companies and universities on a large scale. An example of its use is that the microscope makes it possible to observe the process of cell division in live bacteria. Before the invention of the phase-contrast microscope, one could only view cells properly after using dyes, but these kill cells.

We still use the phase-contrast microscope in the laboratory every day. For example, we look at whether cells are dead or alive, how immune cells attack bacteria or what makes tumour cells move.

Nienke Vrisekoop
Assistant Professor, Lab of Translational Immunology, University Medical Center Utrecht


Caroline Bleeker devoted herself to women's equality. She was a scientist at a time when this was still an unpaved road for women. The founding of her own company made her an independent entrepreneur. She hired male AND female employees for her factory. In the NEDOPTIFA publication, she had a special category for women.

Utrechtse Muurformules

Caroline Bleeker is the first woman in the Utrechtse Muurformules: an initiative of physicists Ingmar Swart and Sander Kempkes to give Utrecht scientific discoveries more fame. There were already murals about the Doppler Effect by Buys Ballot, the Random Walk by Ornstein and the Stereochemistry by Van ’t Hoff. In Utrecht Science Park, a building is named after Bleeker: the Caroline Bleeker building is the home of Scientific Instrumentation of the Faculty of Science.