Tattooing is not a contraindication for donating blood. The risk involved with tattooing is of transmission of blood borne viruses. Before accepting you as a potential donor, you will be screened for such diseases through a blood test. It also depends on the time interval between you got your skin inked and now when you wish to donate blood. A minimum of 6 months interval should be there to detect the virus in the blood, if at all there was a transmission during the process of tattooing. The risk of such viral transmission is minimal if you got the tattoo at a good center. Hope it helps you.