Black deposit on the solder after the vinegar cleaning run?

[PuffingBilly]

I've made the copper pot "moonshine" still but when I made the first cleaning run with the vinegar (I used the diluted glacial acetic acid) I've discovered that the internal surface of the pot is covered with the black streaks and the solder has the black "oily" deposit, which are hard to remove (I tried citric acid with a little success).
To make a stil I used the tin-copper solder (lead free) - Sn97Cu3, which is used for plumbing usually. And I didn't expect to find the deposit, which looks like a car grease (see the picture).
What did I wrong? Maybe I used the wrong solder?

[OBX Phantom]

What kind of flux did you use? If you used a petroleum based flux instead of a water based flux, then it is going to feel greasy, and be hard to remove.

[PuffingBilly]

What kind of flux did you use? If you used a petroleum based flux instead of a water based flux, then it is going to feel greasy, and be hard to remove.

I used the soldering paste (Viega Lotpaste Nr3 - made in Germany), which contains the flux and the solder S-Sn97Cu3. I don't know whether it is petroleum based flux or the water based one.

[Doubler]

Was the flux like vaseline (petroleum based) or like a lotion (water based)?

[OBX Phantom]

Read the can, it will tell you which it is made of. Judging by the description of the residue left in your pot, I would say that the flux is petroleum based. If so I would try wiping it out with a rag and either some lacquer thinner, or acetone. Both will evaporate away and not leave any residue.

[The KYChemist]

Brasso would probably work, also, if all else fails.

[Doubler]

After my first cleaning run I used the high proof liquor to clean anything I though needed it.

[PuffingBilly]

Read the can, it will tell you which it is made of. Judging by the description of the residue left in your pot, I would say that the flux is petroleum based. If so I would try wiping it out with a rag and either some lacquer thinner, or acetone. Both will evaporate away and not leave any residue.

The description of this solder paste is fully in German, so I've spent some time for translation and googling the internet. As I understood, the solder paste consists of lead-free solder (Sn97Cu3) and flux Type 3.1.1.C:

Soft solder paste S-Sn 97 Cu 3 + 3.1.1.C
in accordance with EN 29454-1, DVGW worksheet GW 7, DVGW-Reg.-No. DV-0101AP2021

This type of flux is: "... for soft-soldering of leaded tin plate and sheet for tin plating of copper and brass, not suitable in electrical engineering and electronics (containing zinc chloride, irritant)". Probably it contains also the ammonium cloride. It's corrosive and is water soluble.

But what I noticed this morning: the soldered seams on the outside of the pot are also with a thin black coating, which can be smeared when I swipe the seam with my finger. I tried to clean the seams with a metallic sponge and a hot water but when the seam dries and then I wet it again, this thin smearing black coating returns back on the solder

[Maritimer]

If it is petrolatum-based, toluene will remove it easily. A common grease-based flux in North America is Oatey, which I had a lot of trouble removing until I discovered toluene. Acetone, vinegar, and steam didn't touch it. What you are describing sure sounds greasy!

M

[Bushman]

I would do another sacrificial run and make sure you also allow it to steam clean for part of the run.

[PuffingBilly]

After some thoughts I decided that this black deposit was a reaction of the tin to the hot glacial acetic acid. Maybe I put too much of the acid for the first run.
Anyway I cleaned the pot as hard as I could and started to use it for the moonshine. And after all my subsequent spirit runs I didn't see such deposit again.

[shadylane]

Thanks for posting the follow up puffingbilly.
Too many posts end without anyone knowing what the out come was.

[The KYChemist]

Thanks for posting the follow up puffingbilly.
Too many posts end without anyone knowing what the out come was.

+1... I saw this pop up, and was glad everything has worked out for you.