The article presents tests involving natural cracks, including measurements of the width of cracks and the profile of their surface roughness. The investigation also involved tests performed in order to observe how a given factor affects development times in penetrant tests as well as to determine what time of development is recommended for nickel and its alloys in order to detect unacceptable welding imperfections (cracks). The article also discusses the effect of penetration times on the duration of development times and sizes of indications in penetrant tests.