Fire Stain

[HMPjewellery]

hello.

I have a question that I have been worried about asking as I feel I may just be missing a simple trick or just being a bit dense. Haha.

I occasionally get Fire stain on my pieces and even after plenty of filing/sanding it refuses to budge. Currently working on a larger surface area and it sticks out like a sore thumb.
WHY do you get fire stain? and HOW do you get rid of the little blighter?!

Hope you are all having wonderful days xx

[ps_bond]

Why is time at temperature... The longer you spend at soldering temperatures, the more sub-surface oxide you get. The problem is that you're also depletion gilding the metal, so when you've scrubbed down to the area you can see, you've exposed a bit more. It will come out, but it takes some work. Water of Ayr stones help - I keep meaning to find if any of the EDM stones break down in a similar way.

[Dennis]

Hi HannahMary,
The higher the polish, the more the firescale shows, so you do have the option of settling for a satin finish. You can also do depletion gilding, as Peter mentions, by heating and pickling repeatedly six or seven times. This leaves a very thin layer of fine silver on the surface, so covering the fault. Other remedies are:

1. Sending it away for professional plating, which will be thicker and more durable.
2. Scouring until the stain has gone, which can take an hour or so. Using a large green Scotchbrite mop on a polishing lathe is quicker.
3. Firescale can also be removed with dilute nitric acid; not so good at home.
4. Applying a reducing agent as a preventative, prior to heating. An example is a saturated solution of boracic acid powder in meths ( take care to leave your bottle and brush out of range of the flame). Using a more bushy flame also helps.

As you will have gathered, any remaining firescale is difficult to see until you achieve a high polish, so you have to keep retracing your steps. Some jewellers suggest looking for it through a piece of grease proof paper or baking parchment, but I have not tried that. Dennis.