Casewell LT sealer dye leech

[blackcote]

I thought I had it figured out. I had much trial and error prior. I got my part to dye a beautiful dark jet black. So I proceeded to try to seal using casewell's lt sealer. When I dipped it in... some black dye came off which I thought was normal. So I left it in for 10-12 min and when I lifted it out it was dark grey... aaahhhh... that's not what I put in there. the dye continued to leech or fade out of the part. you could see the dye suspended in the solution.

So my question is... are there any experiences like this? Is the sealer not compatible with the black dye? What other causes could there be? How critical it the temp of the solution? I was a couple degrees above the high point printed on the sealer bottle.

Side question... Can you continue anodizing a part if you haven't sealed it but have let it dry?

[Fibergeek]

Assuming that you used a dye intended for anodizing, and that you dyed at a temperature reasonably close to 140 deg. F (like +/- 15 deg. F.) you are seeing the classic symptoms of an anodize layer with a pore size that is too large.

What you describe is a pretty common error, it has nothing to do with sealing.

Anodic coatings that have excessive pore size adsorb the dye readily, but it rapidly leaches out in the pre-dyeing water rinse and/or the sealant bath. If the problem was an inadequate anodic layer thickness, a deep color cannot be obtained.

Excessive pore size is caused by one or a multiple of these:

1. Too strong an electrolyte concentration.
2. Too low a current density.
3. Too high anodizing bath temperature.
4. Indirectly; too long an anodizing time, where dissolution is widening the pores.
5. Indirectly; poor or degraded electrical connections, if constant voltage (CV) anodizing is used instead of constant current (CC). This can make the effective current density much lower than what you set it at.

When the pore size is correct; the work will dye readily, to a very deep shade. Very little dye comes off in the rinse or sealing, certainly not enough to change the shade any. What does come off is mostly dye left on the surface, not in the pores.

It is possible to continue anodizing the work after it is dyed, but not sealed. This isn't likely to "fix" the pore size problem, and you will get dye in your anodizing tank. Not good if you wish to use different colors.

[blackcote]

My dye is from caswell also so yes it is intended for anodizing.
Temperature of dye was about 110... Caswell literature states on page 120 under section "dying the anodize" that... "Dyes are designed to operate at 140deg F, however, we have found most of our dy will work at room temperature, providing you are using our new parameters for power and attaining PAR. After refiguring my current and time I believe you are correct about pore size being the problem, but after redoing my math pore size should have been too small and not taken the dye very well... see my math below

Excessive pore size is caused by one or a multiple of these:

1. Too strong an electrolyte concentration.
2. Too low a current density.
3. Too high anodizing bath temperature.
4. Indirectly; too long an anodizing time, where dissolution is widening the pores.
5. Indirectly; poor or degraded electrical connections, if constant voltage (CV) anodizing is used instead of constant current (CC). This can make the effective current density much lower than what you set it at.

I did rule out 1,3, & 5 and i think 2 (see below), 4 I'm not sure on.

Here's what I have.
6061
.32 sq ft
CC power supply set at 5 amps (I don't remember where I got that number)
threaded connection
to get my time i used 900amps per min / 5 amps = 180 min per sq ft
then 180 min per sq ft * .32 sq ft = 57.6 min
actually it anodized for 70 min. (could this have been too long and the anodic film was being worn away.)

So do I figure right that I was anodizing at 5 amps/.32 sq ft for a current density of 15.625 A/sq ft wow, if that is right i had not intended to be nowhere near that. Although they say that the standard way is 12-18 A/sq ft.

So to get my current density to 4.5 amps / sq ft... I need to turn my current down to 1.44 amps and anodize for 200 min wow.... i'll be waiting a while. Maybe i'm way off on current densities though. I can't seem to find anywhere that explains how to figure them.
Can anyone confirm or correct my numbers?

How do the numbers work with more than one piece? Can you just add the areas together and plug them into the equations?

It is possible to continue anodizing the work after it is dyed, but not sealed. This isn't likely to "fix" the pore size problem, and you will get dye in your anodizing tank. Not good if you wish to use different colors.

Really was only a curiosity question... I was thinking of bleaching it then re-anodizing again for longer period. But I think I will be better off stripping it and starting with a fresh layer of aluminum.

Thank you so much for the thorough answers.

[Fibergeek]

I can see by your post that you did your homework, anodizing is like everything else in Life, you get out of it what you put into it.

I agree with your proposition that you anodized too long. Don't underestimate the evil effects of excessive dissolution. But ironically; if you stopped dissolution entirely, you wouldn't form a suitable anodic layer at all.

I've heard this "900 Amps/min./sq.ft."stuff before. I have verified that the "720 Rule" is quite accurate since I can measure anodize thickness. That means replace "900" with "720". The 720 Rule is based on real electrochemistry (it has a provable mathematical base) the 900 stuff is from some amateur's website and has no basis at all beyond his particular setup. If your setup isn't identical to his (fat chance) it isn't likely to work. His connection method is poor, and he doesn't use CC, the 900 stuff is a fudge factor to compensate for this.

You are correct in saying that you actually anodized at 15.6 A/sq.ft.. If you were using LCD electrolyte, the pores would have been smaller, not larger, not so small to make dyeing too difficult, just harder than it should be. This leaves excessive dissolution, and its characteristic of opening up the pores to too large a size. The 110 deg. dyeing is an error in the documentation, Caswell is been slow in correcting errors, but I expect that to change.

On what basis do you rule out #5? Threading is no guarantee of a good connection, its mechanical and is prone to failure just like any other mechanical method. We could verify connection quality if you provide some voltage measurements during anodizing.

Multiple pieces add in surface area, as you surmise.

[blackcote]

I can see by your post that you did your homework, anodizing is like everything else in Life, you get out of it what you put into it.

Thank you. Apparently not enough homework. I hope to get a lot out of this as it is already taking up more family time than I had intended.

I've heard this "900 Amps/min./sq.ft."stuff before. I have verified that the "720 Rule" is quite accurate since I can measure anodize thickness. That means replace "900" with "720". The 720 Rule is based on real electrochemistry (it has a provable mathematical base) the 900 stuff is from some amateur's website and has no basis at all beyond his particular setup. If your setup isn't identical to his (fat chance) it isn't likely to work. His connection method is poor, and he doesn't use CC, the 900 stuff is a fudge factor to compensate for this.

You are correct that this is off a website... an old one now. after checking again it's been updated to the 720 rule now.

So using 720 my time should have been 46 min. Then I agree with the dissolution argument. On the previous attempt I tried .36 sq ft for 40 min. but the dye didn't take to well got nice even grey color, but I wanted black so I didn't bother sealing it. 52 min is the calculated time but I've read that 1/2 to 1/3 of the time is enough if color is the only concern and not thinkness or hardness... is this not the case also? Based on the dissolution problem of the previous piece I suspect my electrolyte temp wasn't high enough. My thermometer is only graduated down to 75. But it read just below there the whole time. It must be much more inaccurate past the graduation markings.

And on that same run my CD would have been 13.9... correct? Both 15.6 and 13.9 should be acceptable since I'm not using the LCD electrolyte. I want to keep my times down as time is money so I didn't want to use the LCD setup. Is there any way to verify what your solution ratio is? and what the effective high and low CD limits are? I have a borrowed 0-40A 0-40V power supply. I don't intend to do this yet but in an effort to shorten anodizing times I could increase current density... correct? to what extent? And I would need to increase my acid to water ratio... correct? What happens when you run higher current densities but not higher solution ratio's? What risks or disadvantages are there to doing this?

You are correct in saying that you actually anodized at 15.6 A/sq.ft.. If you were using LCD electrolyte, the pores would have been smaller, not larger, not so small to make dyeing too difficult, just harder than it should be. This leaves excessive dissolution, and its characteristic of opening up the pores to too large a size. The 110 deg. dyeing is an error in the documentation, Caswell is been slow in correcting errors, but I expect that to change.

So my next attempt will involve getting a thermometer that will read below 75 for the electrolyte, use the 720 rule instead, get my dye temp to around 140, and use 12 ASF for current density (maybe?)

I'm still unsure of what current density I should be operating at. I know it should be whatever works... but how do I get close in the first place?
Is there anyway to check what ratio of the electrolyte is? I mixed it up a while ago and forgot what it exacly was... either 1:1 or 1:2, but I can't remember. I'm sure this info would help me determine a suitable current density to run at.

On what basis do you rule out #5? Threading is no guarantee of a good connection, its mechanical and is prone to failure just like any other mechanical method. We could verify connection quality if you provide some voltage measurements during anodizing.

Sorry I can't quote voltages as I wasn't watching closely, If I had to guess it would have been around the 15V +-. What does this mean for connections? Is this where the 2.5 ohms comes in? But that only applies to the LCD setup... correct? What would I be looking for with a more dense solution?

My head's full for today. Whoever said anodizing is easy and forgiving was a little off. Maybe once a person gets all this sorted out it is but getting there is a rocky road.

[Fibergeek]

Anodizing looks so difficult now because its new to you; don't worry, you will get the hang of it, and it will become easy and predictable.

Keep in mind that LCD was developed (by me) to minimize equipment costs and maximize safety. It was intended for hobby use, it by necessity (to keep it safe and cheap) is too slow for most commercial applications. That said, its an excellent way to learn anodizing. When you understand the anodizing process you will be able to see how you can modify it for commercial application. This approach will get you up to speed quicker and cheaper than starting with standard anodizing and struggling with it.

You can get a battery powered digital thermometer with a remote temperature probe for about $20. It will be much more convenient to use as well as being far more accurate.

I suggest that you carefully read the sticky at the top of the page, A question about the Old Method I think this will answer your electrolyte vs. current density questions.

If you use LCD current densities (3-6 A/sq.ft.) with substantially stronger electrolyte you are favoring dissolution at the expense of coating growth. This could cause dye retention problems all by itself. You can use LCD electrolyte at higher current densities without too much trouble, but not the reverse.

The range of bulk coating resistances observed depends on electrolyte conductance. This means that stronger electrolytes conduct electricity better than weaker ones. 2.5 A/sq.ft. corresponds to LCD electrolyte, standard electrolyte concentration will be about half of that. Better conduction is not necessarily a good thing, again, read the sticky. A downside to stronger electrolyte is that its more noxious and more corrosive (read the sticky).

Measuring the electrolyte concentration will be more chemistry than you will need or want to mess with. Hydrometers don't work well after you get some aluminum dissolved in the electrolyte. Keep a notebook and write this stuff down as you do it, it will save you lots of time in the long run.

Did I mention to read the sticky?

[blackcote]

Thanks. I've done that and still can't get it. One more try tomorrow.

[neilfj]

According to your other post about using tap water, all Fibergeek's responses won't apply. Tap water will interfere (at a minimum) or prevent anodization depending on its chemical makeup. If you think about common chemicals found in tap water, such as chlorine, flouride, iron, copper, lead, tin, arsenic, selenium, etc., you can see why it would cause problems. Even small amounts of these chemicals will affect anodizing and dyeing. Tap water should never be used when anodizing.

[M_D]

On the part that looked good but faded in the sealer, how fast did it start to soak up dye and how long did it take to get dark?

[blackcote]

i believe it was pretty fast like 10 min or so. I left it in there for 20. See my next post to the distilled water thread for some knock your socks off numbers. By the way distilled water didn't work either. I don't think dying is the issue anymore. Something else is going on. I have another experiment that I'd like to try.