Ron posted this awhile back for cleaning up castings. He also gave an excellent demonstration at the Oregon Gun Makers Faire and in his seminars.
CUTTING CAST ENGRAVING
Ron Scott 2022
Even the best quality casting with decoration will benefit from some amount of refreshing. Castings created from original parts often suffer from some amount of wear and hence, lost detail. Additional detail is lost in the process of creating a mold, shooting a wax; and investment casting. This is true, whether the cast object is high, mid or low relief or strictly engraved. I will attempt to share the process I have adopted in refreshing decorative details. How much recut you do is dependent on how much detail is fuzzy and the amount of time you budget into the project. A surprising improvement can be made by simply recutting the major outlines of figures and borders. Better results occur when all details (shading) are added. The most dramatic improvement includes the retexturing of relieved backgrounds in addition to the aforementioned recuts. I will list my process in order of work.
Straighten casting and remove casting sprues.
File and polish any areas that are smooth, without engraving.
Pickle part in white vinegar or similar acid to remove casting oxide (2-4 hours).
Scrub with baking soda and toothbrush.
Lightly highlight the surface with a polishing emery board (approximately 800 or finer grit). This creates a better read of the engraving.
The visibility of faint lines will be enhanced by using a raking or low angle light.
You may find that some engraving was cut using a narrow angle graver. Many of the ca. 1740s Jaegers appear to have been decorated with gravers of approximately 80 degree angles. I think it is important to retain the character, depth, and width of the original cuts, hence the reason I have gravers in 123,116, 96, 80 and 70 degree face angles. You will eventually find a need for a variety of flat gravers to increase or smooth relieved backgrounds.
I choose to cut the borders and primary figure outline first and proceed to the shading details. Since the cast surface has irregularities, such as pits, bumps, oxide, and even casting investment, you will notice a tendency for the graver to bog down or surge. To deal with this phenomenon, I make a light cut first to get a channel and a second cut to re-establish the width and depth of the cut. Shading cuts are often accomplished with a singe pass.
If one of your cuts has created a sharp edge in a figure with round contours, you will need to blend it to match. A ceramic stone retains its form well enough to control the shape of an edge and an extra soft 600 grit oil stone will reshape itself to polish the desired contour. Congress tool is a good source of these.
Relieved backgrounds are most often textured to give a further appearance of depth to the raised elements. While there are other textural styles, I will describe the most common to 18th century Jaegers. This is a stippled or beaded background, accomplished with punch, that features a cup on the point. The stippled background has a surface of half rounds across it. Stipplers in various diameters are available from most engraving equipment suppliers. They are inexpensive and break occasionally, so get several. I would suggest a bit of experimentation with stippling. The needed force of the hammer blow to the punch will vary with the type of metal you are working and if the casting has been annealed. Try to make the pattern of the beads fairly uniform; avoiding overlapping. I set my beads along the corners of a background, around the edges, and then fill the center.
When all the recut and background work are finished, you will likely want to put a bit of gloss to the upper portions. This will enhance the overall illusion of depth. A jeweler’s polishing cloth or a cloth with polishing paste lightly buffed on the surface should suffice. If a more dramatic effect is desired, consider oxidizing the entire object with an antiquing solution or similar material to darken the entire surface. Then buff with the aforementioned cloth.
If the casting is very fuzzy or has deep flaws, you might want to take a photo or a rubbing to record the details before proceeding to the process. This will give frame of reference in case of erasure during the clean up.
I think that you will find a better understanding of the style and tools of 18th century metal sculpting and engraving during the process of recutting a cast object.
I cannot over-stress the value of good lighting. My engraving bench has both direct overhead LED and low angle fiber optic lights. In addition, I can apply a UV filter to control glare.
Magnifying the object in some fashion is pretty much a necessity. I use a microscope designed for engraving. Dental loupes in magnification of 5X or greater would be a good choice.
I hope this brief description is of some assistance in getting started. The demonstration and discussion should help in the overall understanding of the process.
Ron Scott
Hope that this helps. Maybe it can be added to the tutorial section.
William
