tig welding aluminum penetration

[whensparksfly]

how do you know when tig welding aluminum is penetrated right. my welds look good but i want to know they are right. what should i look for
thanks

 

[wheresmejumper]

http://welding-tv.com/2013/06/06/tips-for-welding-aluminum-butts-2g-horizontal-position/

he mentions and shows right penetration

 

[whensparksfly]

thanks found this one too http://welding-tv.com/2012/04/19/aluminum-welding-training-joints-lap-and-tee/