project sparrow etch process

with less than 3 weeks to the deadline it feels as though i’ve pretty much cracked the major technical challenge of the project – the text. i need to etch it clearly and deeply enough to accommodate several layers of enamel while leaving the text proud enough to stone back to the bare copper.

the (expensive!) blue transfer paper i started with was temperamental to say the least. once i switched to the (much cheaper and readily available) yellow paper i got much more consistent results. laser printer toner is effectively melted plastic. once that is transferred to the surface of the copper it acts as a resist to the etching solution.

for the depth of relief i need i found the etch began to cut in underneath the toner resist over time and obscure the text. the solution to this is to add another protective/resistant layer. the blue paper does this in a single pass – both toner and a blue plastic layer are transferred. but i had highly inconsistent results.

toner and foil text on bare copper. black electrical tape prevents the edges eroding in the etch.

my refined process was to press the yellow paper at full heat for one minute (pre-warming the  copper to help with registration) then immediately quench in cold water. after about a minute i carefully peeled the paper still under the water to get a virtually flawless transfer. i then re-coat the piece with hot foil – which attaches only to the toner. this double layer gave me a tough enough resist to take an hour of hot etching.

bain-marie with support

suspending the piece in the etch was another challenge. it needs to be face-down in the solution, to allow the ?salts? produced in the reaction to fall away and produce a deep etch. double sided tape and blue foam was a failure – the heat melting even the strongest tape. i finally worked with a stand inside the solution. the roughly cut surface needs to be uppermost otherwise obvious rings appeared where the piece touched the support.

fresh – brown – etch bath

i also found that the etch exhausted much quicker than i expected. the used solution turns from brown to bright green when saturated with copper. i found each batch would last for max 1.5 pieces. i kept the temperature up with a bain-marie made up with virtually boiling water in the large container, which would stay warm enough for one full piece.

finished deep etch – foil has dissolved but black toner remains
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