Etching Gradients in Copper Alloys

[David Durman]

I have a long term bronze project I am working on and want to pick everyone's brains about something that occurred to me about the etching I will be doing at some point. I am planning on etching flowers into the surface of my bronze and I thought it would be possible to create a gradient on the petals with my etchant. Essentially, I would apply my resist everywhere but the outline of the flower area; after a short dip in some ferric chloride I would take it out, clean it off, and apply resist to the areas inside the flower design that I want to be the most raised. Then another quick dip, cleaning, and widening of the resist area; I would repeat this until I etch all the way to where I want the deepest etching. In other words, I would create consecutive, concentric etches that I can smooth out post-etching to give a 3-D texture to the design. Does this sound reasonable, or is it wildly impractical? Somewhere inbetween? Would it be better to try to carve out the design with a Dremel? 

[ThomasPowers]

Known process just time and labour intensive.

[David Durman]

So it is a sound method and doesn't have some critical flaw that I am not thinking of?

[ThomasPowers]

Try it on an experimental piece and refine your resist and etchant processes.

[David Durman]

A fair point; I can try it on one of my bronze ingots, although I'll have to bear in mind that those are 12.5% tin and what I'll ultimately be etching on will be 8%. I suppose I could cast a separate block just for etch-testing.

[draavi]

This is similar to the processes used for embossing and engraving plates in printing.

You completely coat the object with the resist, then draw the first lines of what you want etched into the resist, eliminating it down to the surface.  Then after the first dip, you continue to draw your pattern a level/layer at a time.

The parts that were drawn first will be the deepest.

As Mr. Powers stated experiment on a piece first.

[David Durman]

Huh. That is essentially the same method, just done in reverse of what I was thinking. Seems like it would be better to use that order. I am hoping that the end product will be sufficiently smooth (with minimal sanding) for me to gild the design as well; it might be easier to simply use a Dremel but I would be nervous about the consistency of hand moments on such a fine scale, preferring to leave it to much more controllable chemical processes.

[Alan Evans]

Could you not rely on conventional drawing techniques to generate the 3d image? Using cross hatching or different sized dots for depth shading as one would normally with engraving or chasing.

I would have thought that you will be hard pressed to differentiate the various surface levels achieved unless you are viewing with particular side lighting conditions...or you are reckoning on acid forming / carving rather than just etching a design on the surface. Acid erosion as in spark erosion perhaps...

The gilding would also tend to flatten any depth variation.

If you are wanting to produce an actual low relief image, have you considered chasing or engraving with punches or gravers rather than a dremel?

As far as sanding afterwards goes I would have thought that it was a total no-no. You would obliterate any detail you have managed to generate. Ideally you should be starting from a perfectly finished surface and then the etched areas are visible in contrast to it...All subtlety and the fine details possible would be lost if you start abrading it after etching.

Only you know what you have in mind as an end result. As said above...trial and error / experimentation is your best guide.

Alan

[David Durman]

I briefly thought about using punches and gravers, but I am reluctant to rely on my (relative) freehand ability over passive processes, such as image transfer and chemical etching. I had planned on allowing the etchant to cut deeper than one normally would on each pass, creating a significantly recessed image rather than a simple transfer of the image. The images I am looking to transfer are the attached daisies for one item and the attached marigold for another; ultimately I want to have the petals of the daisies in silver gilding and the center in gold, the marigold petals in a silver gilding with colored edges like the image (I am still debating these internally). The ring and knife blade images are simply google image results that show the approximate depth I am thinking of; do you think this is achievable? I am reluctant to purchase engraving tools and try my amateur hand at it; I would be happy to learn, but these particular items are a fair bit important to me and I simply hate leaving anything to chance. Thanks, though; it definitely gives me something to think about.