imago corvi

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Guilloché

Rose Engine

Rose Engine

Guilloché  is a term for a pattern that has been applied by a hand turned engraving machine, such as a rose engine. These machines are quite rare now – but the few remaining technicians are passionate about their art. A rose engine is a specialized kind of lathe. The headstock contains a small engraving tool. It rocks back and forth controlled by a gear moving against a rosette while the lathe spindle rotates. The gear is turned by hand and the pressure on the engraving tool is guided by hand. It takes a great amount of skill to control the machine. Rose engine work can make flower patterns, as well as convoluted, symmetrical, multi-lobed organic patterns. Sort of like a complex spirograph in metal. 

Recently I met a gentleman from Burlington Ontario who has one of these machines and a passion for turning. he was also aware of the tradition for enamelling guilloché , and was interested in learning some techniques.

trapped bubbles

So I did some research and we spent a day trying some different techniques with good success. The problem I had run into in doing some preliminary samples was tiny trapped bubbles. In most enameling applications this is not a serious problem, as they are not usually obvious, and they decrease with repeated firings. However with the fine pattern of guilloché , the bubbles obscured the design and the typical single firing required the bubbles to be gone in the beginning. It was also important to fire the back and front at the same time, as turning the piece over to fire the back would result in trivet marks, and firing the back first would anneal the front and take the edge off of the fine engraving cuts.


The advice that I had gotten was to use very fine (325 mesh) grounds. This was directly against the perceived wisdom among enamelists that bigger grains give more clarity. 

test piece

Some enamelists use only 80 mesh grain for clarity – in my own pieces I generally use a mix ranging from 200-80 mesh. I feel that a variation in size will minimize the trapped air bubbles by preventing the “boulder effect” (the theory that large grains only will trap more air) 

under-fired – oxides trapped in cuts

So the process we worked out was to sift enamel on the back that was saturated in gum binder, and then turn to the front and wet pack 325 mesh enamel tightly but thinly on the front – and do a very high firing (up to 1600 for 2 1/2 min) when the piece was dry. We tried grinding the enamel from lump form to see if the results were any better, but concluded that it wasn’t worth the trouble.

 

Different colours will require different times/temperatures, but I think he has enough information to go forward  with confidence and produce some really beautiful enamelled guilloché 

Light green on fine silver

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This entry was posted on May 11, 2011 by in enameling, teaching and tagged , , .

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