need help finding problem....

[Sid03]

I did two pieces yesterday at the same time. One I dyed orange and it turned out fine. The other I dyed red.....

While dying and after removing from teh dye bath(while still wet) it looks 100% fine. When it started to dry it got darker spots on it.....dull looking compared to the other area's. You can rub your finger over the area and it will change color and you'll get red chalky powder on your finger very easily. Any idea's offhand? I can post teh total spec of the whole process I did if needed later, but everything is the same and I just had a piece turn out in red perfect last week. My final PAR turned out to be 2.66ohms. Parts werent sealed so thats not a variable. The part was in the red dye alittle longer then normal....about 20 minutes, if that would effect anything. Thanks!

[Sid03]

no ideas? This randomly happens to me all the time and I would LOVE to know exactly why. I can take pics if needed....and if I can host them somewhere.

[Fibergeek]

If this "randomly happens all the time" something is marginal. Since none of us can see what you are doing, maybe you should lay out your entire process. BTW, does this only happen with red?

[M_D]

Maybe you could post pictures to the album area? If you do that and list the entire process in detail, maybe someone will have answers that will help you. What is your red dye ph now? It will change sometimes, so just because it was ok, don't assume it is now.

[Sid03]

i emailed the pics to caswell, i believe they will be posting them for me.

[mcaswell]

[NeoMoses]

Looking at those pics, it doesn't immediately appear that anything is seriously wrong.

You state, "When it started to dry it got darker spots on it.....dull looking compared to the other area's." That's normal, an unsealed anodized surface will be somewhat rougher than the original part, and when the dye starts to dry, the dry areas will appear 'dull' while the wet areas will appear shiny.

"You can rub your finger over the area and it will change color and you'll get red chalky powder on your finger very easily." Again, that's pretty normal. Rubbing your fingers of a dry, unsealed part will allow you to pull dye out of the pores, eventually changing the color. You can also leave oily fingerprints on the part if you touch it between the dyeing and the sealing step.

Did you seal this part, or just let it sit? If this part was acting this way after 15-30 minutes in the sealer, then there is likely a problem with excessive pore size not allowing the part to fully seal. That's usually a function of your anodizing parameters (Current density, electrolyte concentration, temperature...)

From looking at the pictures, it appears there is an anodized layer and the part did not lose electrical connection. What was the surface finish before putting the part in the tank? Did you alkaline etch these parts (Lye or Desmut) before anodizing?

[Sid03]

Caswell degreaser and desmut used before ano.

What you mentioned is in no way normal. I can take parts that I dont seal and rub and nothing comes off. It's not like im really rubbing on this part....one pass of the finger gets your finger red like in the pic. When I gave the wet/dry comparison, i meant when the part was completely dry. The part was completely dry in the pics...had been sitting for days. You can see how some areas are duller looking, and the chalky residue rubs off ALL of the areas very easily.

Any ideas?

[M_D]

This may or may not be the problem: It may be the part is anodized for too long or at too high of a rate. If you have extra test pieces of aluminum you might try experimenting with times. As far as why the orange looked ok and the red didn't, I know different colors have their own distinct characteristics, although I haven't used orange and can't comment on it specifically.

[whistule]

I would have thought the colour rubbing off wa because it was a residue on the surface that had not been absorbed into the pores. I had one or too problems like this when starting out and in my case I didn't have enough agitation in the dye tank and the dye was slightly too concentrated.

[Sid03]

i have no agitation in the dye tank, and didnt know that i should. Is this a big issue?

[whistule]

That's certainly what caused the problems in my case. I just use an airline into the bottom of the dye tank from a aquarium air pump. Another step forward was to heat the dyes - not sure if you do this - and I don't think it'd the cause of your problems but it does help the dyes to be absorbed into the pores.

[Sid03]

yes, i do heat the dye tanks to 140 degrees. Does everybody use agitation of some sort in their dye tanks? Any other input into this?

[M_D]

I haven't noticed any tendency towards a chalky finish in my work, except on parts that were anodized for a very long time. There appears to be some time limit where the anodizing gets very strange. When anodized for a long period the parts soak up dye well, but the anodizing layer is not good. I have seen evidence that one layer builds on top of another one. The parts look good until they dry, and when sealed get worse. I have intentionally over anodized for experimental purposes.

I will keep the thought about the dye tank causing problems filed away, as it may be useful for me to troubleshoot a problem latter.

As with heated dye, I have noticed parts also dye faster with agitation; sometimes just stirring them in the dye by hand accelerates the dying. If the tank is heated, agitation is useful to keep the temperature even, as the upper layer tends to get much warmer than the bottom. If the quality of the anodizing is conducive to rapid dying, and the dye temperature varies too much from top to bottom of the part there can be banding or a gradient effect. If left in the tank long enough, the parts seem to even out, but if you aren?t shooting for a deep color uneven dye temperature could be particularly troublesome.

[Fibergeek]

I concur with M_D.

The chalky stuff is the outermost anodization, undermined by dissolution. Notice how it looks orange under the wiped areas, where the dye hasn't fully penetrated. Excessive dissolution can so weaken the anodize layer that some of it can be rubbed or wiped off, it just crumbles. If you measured the coating thickness you will see that it is noticably thinner than a sample done under similar conditions but was not subject to excessive dissilution.

I also concur that this was probably caused by too long an anodization time for your particular set of anodizing parameters, this is the most likely cause. Other things that can cause this are too high an electrolyte temp., too strong electrolyte concentration, too low an ACTUAL current density (reasonably accurate measurements are important). Agitation in the anodization tank effects how even the coating thickness will be, not dissolution rate. Agitation in the dye tank is certainly helpful.