Color depth vs. anodizing time:

Intro:

I've been playing around more and more with constant current anodizing at 12 A/ft^2 in a 1:1 (battery acid:water) electrolyte tank. My test pieces are 0.25" 6061-T6 rod, 6" long. Surface area is 0.0334 ft^2. All test pieces are bead blasted, then cleaned in dish soap, then Simple Green before anodizing.

I am testing color depth vs. anodizing time. Having no equipment to accurately measure the anodized layer thickness, I theorized that relative layer thickness could be judged by color depth. That is, the part with the thicker anodized layer, (assuming all else is equal) will have a richer, deeper color.

Correct me if I'm wrong, but as I understand the LCD anodizing paper, layer thickness can be judged by the anodizing voltage or resistance, thus the reasoning behind monitoring and detecting PAR. Once the peak voltage has been reached, you have reached the peak layer thickness.

So... in theory there should be little to no difference in color between parts if the same voltage is reached each time you anodize. (Again, assuming all else is equal). To test this theory, I first anodized a part to PAR (slightly beyond, actually, just to ensure PAR was actually reached). This first part was anodized for a total of 45 minutes, yielding the below Voltage:Time plot. Using the first V:T plot, a suitable time would be selected for the second test piece. 20 minutes was selected, as it would give 97% of the peak voltage reached in the first test.

Now to the results. Here's what I've seen so far:

As you see, these graphs look much like the LCD graphs at 4.5 A/ft^2. Anodizing to PAR with the first piece took approximately 28 minutes, yielding a peak voltage of 15.2 volts. PAR then would be 15.2/0.4 = 38 Ohms. Normalized per unit area gives ~ 1.27 Ohms/ft^2. Why is this number not 2.5? Keep in mind the acid bath is much more concentrated than LCD.

Here's a picture of the finished parts:

The part on top was anodized for 20 minutes, the part on bottom was anodized for 45 minutes. As you can see, the part that was anodized for 45 minutes achieved a deeper blue color. Both parts were submerged in the same blue dye at 120F for 15 minutes, but had reached their full color within 5 minutes.

Results:

- It is clear that the part that was anodized for 45 minutes achieved a darker color, possibly indicating that its anodized layer is slightly thicker.

- The part anodized for 20 minutes, although not as dark as the 45 minute part, did achieve a good solid anodized layer that took color well.

Fibergeek, I'm especially looking for your input on this. Does the above sound correct? What methods are available to accurately measure anodized layer thickness?

Intro:

I've been playing around more and more with constant current anodizing at 12 A/ft^2 in a 1:1 (battery acid:water) electrolyte tank. My test pieces are 0.25" 6061-T6 rod, 6" long. Surface area is 0.0334 ft^2. All test pieces are bead blasted, then cleaned in dish soap, then Simple Green before anodizing.

I am testing color depth vs. anodizing time. Having no equipment to accurately measure the anodized layer thickness, I theorized that relative layer thickness could be judged by color depth. That is, the part with the thicker anodized layer, (assuming all else is equal) will have a richer, deeper color.

Correct me if I'm wrong, but as I understand the LCD anodizing paper, layer thickness can be judged by the anodizing voltage or resistance, thus the reasoning behind monitoring and detecting PAR. Once the peak voltage has been reached, you have reached the peak layer thickness.

So... in theory there should be little to no difference in color between parts if the same voltage is reached each time you anodize. (Again, assuming all else is equal). To test this theory, I first anodized a part to PAR (slightly beyond, actually, just to ensure PAR was actually reached). This first part was anodized for a total of 45 minutes, yielding the below Voltage:Time plot. Using the first V:T plot, a suitable time would be selected for the second test piece. 20 minutes was selected, as it would give 97% of the peak voltage reached in the first test.

Now to the results. Here's what I've seen so far:

As you see, these graphs look much like the LCD graphs at 4.5 A/ft^2. Anodizing to PAR with the first piece took approximately 28 minutes, yielding a peak voltage of 15.2 volts. PAR then would be 15.2/0.4 = 38 Ohms. Normalized per unit area gives ~ 1.27 Ohms/ft^2. Why is this number not 2.5? Keep in mind the acid bath is much more concentrated than LCD.

Here's a picture of the finished parts:

The part on top was anodized for 20 minutes, the part on bottom was anodized for 45 minutes. As you can see, the part that was anodized for 45 minutes achieved a deeper blue color. Both parts were submerged in the same blue dye at 120F for 15 minutes, but had reached their full color within 5 minutes.

Results:

- It is clear that the part that was anodized for 45 minutes achieved a darker color, possibly indicating that its anodized layer is slightly thicker.

- The part anodized for 20 minutes, although not as dark as the 45 minute part, did achieve a good solid anodized layer that took color well.

Fibergeek, I'm especially looking for your input on this. Does the above sound correct? What methods are available to accurately measure anodized layer thickness?

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