The nickel-Watts plating solution was produced as described elsewhere. The alkaline copper-plating solution was modified from the cited recipe : For a litre of the solution, basic copper carbonate (30 g) was initially dissolved in etidronic acid (65 wt%; 150 g), and made up to 600 mL with deionized water, before the addition of sulfamic acid (50 g) and potassium pyrophosphate (100 g). The solution was raised to pH 6 by the slow addition of potassium hydroxide (~70 g); gelation occurs at pH 5, which redissolves at higher pH. Finally, potassium carbonate was added until a pH of 9 is obtained (~100 g).