Avoiding Firestain

I was making a set of candlesticks to a slightly futuristic design and knew that if they became firestained then they would be impossible to polish. As such, I needed to come up with a method of application which was better than my plant sprayer, and you can not get mouth air brushes in the UK for health and safety reasons, so I came up with the following simple applicator based on a jam jar and a foot pump. It worked a treat and the candlesticks were displayed at the Goldsmith's Design and Craftsmanship exhibition in 2006.

The finished piece. It holds a reasonable amount of Pripp's and gives a fairly even spray. Controlling with the foot pump mans that you can use it in one hand and your torch in the other.
The device fully laid out. The foot pump is a rescued one, any good source of air would do, from a dingy inflator to a compressor.
The business end. The tube the Pripp's is sucked through is a bit of silver that I had handy, anything non ferrous will do. It has been epoxied into the lid and has an internal diameter of about 1.5mm - I experimented a bit and the kit worked up to about a 5mm ID pipe, but the scale I work on suited this size best.  The nut is metal, but it is silver soldered to a brass screw which goes through the jam jar lid and is fixed with a brass screw, so the Pripp's never touches the iron. The washers you can just see are for fine tuning the height of the air outlet.

The air outlet nozzle is salvaged from a blood pressure measuring kit, but any step down to about a 3-5mm diameter would work as well.

The connection of my piping to the tyre pump. This was a bit of copper pipe I had lying around. I flared and polished the business end so that it fit snugly in the valve clip.
The parts for a belt buckle sprayed up with an even coating of Pripp's using this bit of kit. It now sits within easy access on my soldering station at all times, and I have not had any problems with nozzle blockages or any other technical issues. I would advise giving some thought to the layout of your piping though, as it can get in the way a bit, and the foot pump needs to be well positioned so that it not a trip hazard. Obviously also give some thought to ventilation as a fine mist of boric acid and industrial degreaser probably does not do you any good.