depletion gilding (sterling silver)

[eekoh]

I've noticed when annealing and pickling that I get a milky sort of coating on my sterling silver that can be polished away. I thought to start off with it was some sort of firestain but having read up a bit I've learned that its a layer of fine silver due to depletion gilding.
I understand the process of what is happening (i.e. complete oxidation & removal of the non-silver elements of the sterling alloy) but it would be useful to better understand why since the info i've read says you achieve it by repeated annealing & pickling and i'm only doing it once.

Possible reasons that occurred to me...
Is my pickle too hot? (Small slow cooker usually set to 'high')
Am I pickling for too long? (10 mins ish but longer if dark firescale marks remain)
Is my pickle too strong? (Salt & vinegar recipe, 1tblsp per 250ml)
Am i using the wrong type of vinegar (distilled white malt vinegar as I couldn't buy plain white vinegar locally (I have some on order that should be arriving soon)
Am I heating too much when annealing?

Something else I haven't thought of?

Thanks

[ps_bond]

You get a thicker layer - albeit still not that thick - by repeating the process. A whiteish finish on freshly pickled silver is entirely normal. Doesn't sound like you're doing anything wrong from the description.

[Dennis]

Of course there are benefits to having a fine silver surface:

Depletion gilding is the first stage in adding gold foil for Keum Boo decoration using gold foil.
It gives sharper detail when roll texturing in the mill.
It can cover and disguise small amounts of firescale, which is more deeply seated.
It might be your only finish in hollow objects too small for rotary tools.

Strangely, the myth is perpetuated by tutors and authors that depletion gilding brings fine silver to the surface. As you have rightly said, it removes copper which has been oxidised by heating. Dennis.

[eekoh]

Thanks both, I hadn't realised that the fine silver layer was inevitable. It hadn't been causing any real problem because its always buffed away easily to achieve the finish I'd been aiming for, but good to know that its normal rather than a rookie mistake that could be avoided.

[CJ57]

If you put a piece of silver in the pickle that you haven't heated I think you'll find that it also has the white bloom and it's just the normal reaction of the pickle. Some people like that finish and wish it could be maintained but unfortunately it marks really easily and isn't sustainable