More puzzling events

I was testing a new batch of CuSO4 solution for electrolytic etching on a scrap piece of brass. The result is here:

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I am puzzled at the circular defects which are exclusively associated with the numbers. The only answer I could think of was more bubbles, but why? This is a process that does not generate any gas so unless it is the dissolved air coming out due to heating (about 25W dissipated in the bath) I just cannot explain it. Also, why are the defects present only inside or over the numbers? I do not see them anywhere else.

I have done electrolytic etching with brass before but not a "positive" etch like this one. Never seen a similar phenomenon before.

On the bright side the steel etching is working like magic:

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Michael Koblic, Campbell River, BC

Reply to
mkoblic
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The brass stuff does look an awful lot like bubbles clinging to your resist. How opaque is your CuSO4? Can you visually monitor the process?

If you are using something like vinyl letters for resist, and there is air trapped under the letters then it might expand and come out with heat

-- but if that were the case I would expect some undercutting.

When folks etch circuit boards they gently agitate the etchant, the board, or both -- the two methods that I've experienced personally are to keep tilting the tray with the board and etchant, or to put the board edge-on into a bath that has a bubbler on the bottom.

Reply to
Tim Wescott

snipped-for-privacy@gmail.com fired this volley in news: snipped-for-privacy@4ax.com:

Mike, as is the case with ferric chloride and copper, although the CuSO4 etch is gassless, produces regions of 'depleted' plating solution (in this case, overloaded with zinc salts and copper that hasn't yet joined up with a free sulphate radical).

I suspect, too that there are small convection currents rising from the surface that might cause "cells" much like the granularity you see in thinned aluminum paint, when it's stirred.

In any etching I've ever done that required completely uniform action, I agitated it with a fish tank aerator and an air stone (if the stone was compatible with the solution). Sometimes etching "face down" will also benefit when there are heavier-than-water things crashing out of solution during the process.

LLoyd

Reply to
Lloyd E. Sponenburgh

Gunner Asch fired this volley in news: snipped-for-privacy@4ax.com:

That was odd, but I assumed he'd soldered a thin sheet of brass to a saw blade backing.

He did say he was etching brass, not steel.

It's not out of the question that the conductivity of the whole affair is different over the "cutouts".

Lloyd

Reply to
Lloyd E. Sponenburgh

The brass piece is 2.5"x2.5" of 0.020" stock. The hole in the middle allows a 10-32 screw to hold it to a 1" plastic spacer. The other end of the spacer is attached to the cathode:

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I had the assembly with the anode "face down" i.e. on top as there is a lot of copper chunks falling down on the cathode. I was not observing the process very closely as I have done it hundred times before the same way with other pieces and had no problems. That was, however, using a commercial copper-plating electrolyte. I do not have enough of it so I made a bigger batch from scratch. The main difference: I omitted the sulphuric acid.

I should probably get some and try it again with it as well as watch more closely for the bubbles.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

snipped-for-privacy@gmail.com fired this volley in news: snipped-for-privacy@4ax.com:

Mike, I don't know what picture you think you showed us, but that was definitely a saw arbor knockout (or a perfect imitation of one) in the middle of that brass face.

I don't know of any brass circular saw blades, so I assumed you'd soldered brass to a steel blade.

You need to look at the picture you showed us.

LLoyd

Reply to
Lloyd E. Sponenburgh

This one?

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It's what I said in the previous post.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

snipped-for-privacy@gmail.com fired this volley in news: snipped-for-privacy@4ax.com:

So what the heck is the diamond-shaped object in the middle, partially obscured by un-eroded brass, and partly _clearly_ parted from the body material?

Lloyd

Reply to
Lloyd E. Sponenburgh

Actually it is not a diamond. They are just two lines at an angle (they are really three if you look closely - the right side is a double line). They are lines left over from the previous use of this particular piece which got partly obliterated when I cleaned the piece for this experiment and then got obliterated completely by the etching process everywhere else except in this particular spot where they were protected by the spacer.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

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