The use of good blank fields, regions devoid of stars down to a given magnitude, is crucial for the correct operation of the GTC. So far, the list of deepest blank fields was the compilation by M. Azzaro for the ING telescope. The are not deep enough for the GTC. We have used TESELA, a new VO-tool, to determine blank fields for their use with OSIRIS at the GTC. The result has been a collection of blank fields deeper than those of Azzaro. They will be very useful for medium and large size telescope at the northern hemisphere. In this talk we present this work.