Blue Glow around IN-14 Nixie Tube Digits

My IN-14 Nixie Tube has a noticable blue glow around the digits when powered on, it is mostly visible when the 4,5 digits are on. I Tried changing the resistor as it could be a sign of overpowering the Nixie but no matter what value I used it wouldn't go away or even decrease. I got to the point where I was severly underpowering the Nixie but the blue glow was still very clearly visible. Any Ideas of what this is?

Thanks

Over-powering is always one consideration, but it sounds as if it may be leakage of air into the tube. Time will tell! :roll_eyes: