R.B.
I'm glad to see you're making progress! The color looks great.
As you suspected, you are indeed getting "anode shadow". Electricity always takes the path of least resistance, so the majority of plating takes place on the surfaces closest to the anodes, and not on "shadowed" areas.
However, this part should still plate fairly well:
- 5-6 minutes is not enough time. At .1 A/sq-in, the original formula takes about 40 minutes to build up a .001" plate thickness. Leave it go for 30-40 minutes. The shadowed areas will then have time to plate, just thinner than the outer areas.
- Turn your current down to minimum. Again, at higher currents, more of it will go to the closest parts. At lower currents, it will spread out more. Try .075-.080 A/sq-in.
- Rotate your parts, change the positioning, while plating, so the "shadow" changes position.
Watch the shadowed areas when you do the acid dip. If they brighten up just like the outer areas, then they have plated, and should chromate well.
If after all this, you're still getting shadow, then you'll have to use more (auxiliary) anode. Thin strips shaped to fit close to the shadowed areas.
Sean