Clear anodize thickness

i searched and found hard and black thickness, but nothing about clear. Usually i count on .001 per side for those, bur not sure if clear is any different?

Clear is the same, the dye adds nothing to the total thickness

RJT said:

i searched and found hard and black thickness, but nothing about clear. Usually i count on .001 per side for those, bur not sure if clear is any different?

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"Hard" and "Black" are chalk and cheese. "Hard" typically means Type III, which is generally .001" build (although the anodizer will tell you the thickness is .002" -- .001" penetration and .001" buildup).

Anyway, clear Type III would be about the same buildup as black Type III, .001".

Type I is thinner, more like .0001" buildup, but can be clear, black. or other colors.

HTH.

Mike

The answer to this question is often dependent on what practices your specific plating shop follows, but in working with the same shop for the last 20 or so years, this is what I have found (which largely agrees with Mike above and what my shop tells me):

Type I --- .00005-.0001 thickness buildup, many shops don't do this process well (or at all), and color choices may be limited
Type II -- .00035-.0004 thickness buildup in dyed process, .00025-.0003 buildup for clear
Type III - .0010 typical surface buildup, no observable difference in color vs. "clear". As noted above, the actual thickness for .001 surface buildup also includes similar depth of penetration (.001) into the substrate.

I had also (previously) thought like Moonlight that the dye vs. clear made no difference in Type II process, up until a few years ago, but my plating shop informed me otherwise when I started using them for a lot of clear Type II where there were parts with close tolerance holes. That surprised me at the time, but it was absolutely correct. I assume there is some small variation in process that creates the differential in thickness, perhaps to get a better set of conditions for dye absorption. Another reason to discuss specifics with the shop you plan to use.

generally, type II dyed black will require perhaps twice the time in the anodizing bath as compared to type II clear which could result in thicker coatings. black dye needs more anodic coating to effectively penetrate to produce an acceptable black finish. most other dye colors aren't as demanding as black.

The platers I use say typically Type II clear is .0003-.0007 buildup (approx 1/2in and 1/2 out) and Type II color will be .0007-.001 buildup.

OK, I have to ask. Other than the thickness, what are the differences between types I, II, and III. Price? Process? Possible colors? Durability? etc.

All of the above, which cascade. Cause and effect, you might say.

There's a pretty decent write-up on Wikipedia about the various anodizing processes. Regarding pricing, I imagine that any shop will price the services with Type II being least expensive. Type II and III use similar chemistry (sulfuric), Type I is a chromic acid process, which is a likely contributing reason many shops stopped doing it.

Ooooo.... hexavalent chromium. Wasn't that what the Erin Brockovich movie was about?

Boy, I sure don't want her after me.

mdshunk said:

Ooooo.... hexavalent chromium. Wasn't that what the Erin Brockovich movie was about?

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specfab said:

<snippity snip snip>

I had also (previously) thought like Moonlight that the dye vs. clear made no difference in Type II process, up until a few years ago, but my plating shop informed me otherwise when I started using them for a lot of clear Type II where there were parts with close tolerance holes. That surprised me at the time, but it was absolutely correct. I assume there is some small variation in process that creates the differential in thickness, perhaps to get a better set of conditions for dye absorption. Another reason to discuss specifics with the shop you plan to use.

Click to expand...

Anodising grows a honeycomb like structure. The dye fills the pores of the honeycomb and then the water boil cause the top of the pore structure to hydrate, expand and then close over. This is why it can be bigger than no dye.

The electricity and the acid causes the pore structure to grow, but the acid is also removing the honeycomb at the same time. We can set the parameters so as the pore structure does not grow and just a flat sheet forms. This is hard anodising.

specfab said:

There's a pretty decent write-up on Wikipedia about the various anodizing processes. Regarding pricing, I imagine that any shop will price the services with Type II being least expensive. Type II and III use similar chemistry (sulfuric), Type I is a chromic acid process, which is a likely contributing reason many shops stopped doing it.

Click to expand...

type I (chromic) was especially useful when anodizing assembled parts such as aircraft structures since any residual acid remaining between assembled joints would not cause deterioration. it is difficult or impossible to rinse acid from riveted joints. i've restored a few antique grumman amphibians which were completely chromic acid anodized. it was amazing that after 65 years most of the chromic anodized aluminum was still pristine which led me to believe the chromic process was superior to the sulfuric one.