On 22/03/12 11:11, sheldon_mp_cooper wrote:
> I wonder why more people aren't using it then. It is also mentioned here:
>
> "SUPER CHARGING Ferric Chloride" A new additive to help this etchant be more
> effective!
>
> http://www.pcbfx.com/main_site/pages/tech_support/no_etching_tank.html
>
> and at the link they refer to, I came up with the following info for making
> it:
>
> http://www.polymetaal.nl/beguin/mape/edinburgh_etch.htm
>
> Edinburgh etch mix ratio for copper etching:
>
> 1 liter saturated ferric chloride solution 200ml hot tap water 67 grams
> citric acid powder
>
> or
>
> 32 fluid ounces saturated ferric chloride solution 6.75 fluid ounces hot
> water 2.36 ounces citric acid powder
>
> Citric acid powder is typically available in 3 oz. bottles at beer
> brewing/wine making supply stores in the US.
Citric acid powder is available from the local supermarkets in Australia here.
> "Gradually add the citric acid powder to the hot water while stirring
> continually. Once this has fully dissolved, gradually pour this into the
> ferric solution and keep stirring until you have produced a uniform liquid.
>
> "Good results are ensured at 18 to 20°C, but higher temperatures of
> up to 30°C can further improve biting times as well as the overall
> responsiveness of the mordant (aka etchant). This mordant is exceptionally
> long lasting; a tank filling used daily at the EPW, occasionally topped up to
> compensate for evaporation loss, has been known to remain active for up to
> one year without a significant drop in its biting properties. When
> eventually the mordant acquires a deep olive colour it becomes less active
> and is then ready for replacement and disposal.
The deep olive colour is when to add HCl and use as a long-term etchant.