The Chatter Technique
Wear Safety Glasses
We call it “The Chatter Technique” (TCT) and requires a razor knife handle with a #11 blade and a few minutes of practice. Chatter is basically vibration of a tool caused by lack of rigidity therefore leaving intermittent tool marks. In a machine shop, this chatter is something that is to be avoided as much as possible, but in this case we will use it to our advantage.
Warning; If you plan on using this technique be aware that small chips of plaster will fly. Not necessarily into your eye, but it is a possibility and a good idea and we recommended that you wear safety glasses. You may want to set up a backdrop or a shop vac to at least catch the majority of the chips.
What we are trying to accomplish
Two of the basic proto dressing requirements are to square up and/or flatten a rough stone surface for mating and/or aesthetic reasons. The most common pattern that you will have to deal with is the flattening pattern. A real mason would/will use a claw chisel, which has multiple cutting points that create parallel lines in the stone, to bring the surface down to plane, create a rough pattern to prevent slipping (as in sidewalks or stepping stones), or to create mortar grooves. We’re just trying to replicate the basic pattern or look, and this technique implies hand-chiseled work quite effectively. Window sills and both door and window lintels were typically dressed in this manner.
Here are some examples of prototypical dressed stone.
Using The Chatter Technique
The first thing we need to do is to hold the knife in a manner that causes it to almost be in balance. The key is to hold it lightly and at the right angle of attack, so that when you draw (pull), the knife towards you the knife begins to catch and bounce or chatter on a small scale. If you hold the knife too tight and at too sharp of an angle (<45)
it will have a tendency to pare , or carve into the plaster. The ideal angle is anywhere between 45 and 80 degrees. The closer you are to 45 degrees the more shallow the cuts will be and the farther the chatter marks will be from one another. The closer to 90 and the marks get closer to one another, but then you start sliding or dragging the blade. By varying the angles and force of the blade, one can easily and quickly render the surface of plaster into a close facsimile of hand worked stone.
The knife is held in such a manner as to have it near balance on the middle finger as shown in this example. I hold my knife like this for really laying down the initial surface. Your wrist will move in a circular motion as if you were spreading butter on a cracker.
The thumb holds the knife securely, but loose enough to allow it to chatter. When the knife is held in the proper angle and drawn across the plaster you will notice a “vrrrrtttt” sound and a vibrating sensation. That’s chatter. It’s so easy to do and forgiving that it’s really almost impossible to screw up the technique, however, you can still screw up the part, so be careful not to over do it.
Another Way to hold the Knife
The second common holding position is shown above. The blade is still held in such a manner as to be in balance on the middle finger except the knife is held in almost the same position that you would hold a pen or pencil. The actual motion of the knife is the same (circular), but it is done with the wrist. This method is great for fine tuning and tight spaces.
I highly recommend getting some type of magnification and start playing around with this technique on some scrap plaster and . Also, don’t be afraid to use a pushing away motion as opposed to drawing the blade towards yourself. There really isn’t a wrong way to practice this technique.
Dressing the Plaster
The first thing I do is to lay down rows of parallel chatter marks. The reason I only worked one side is to show the difference in “as cast” and dressed.
This shot shows the stone after “cross-hatching”. By rotating the subject 45 degrees the chatter marks really begin to resemble the marks left by scale chisels. It’s not absolutely perfect, but pretty darn close. Close enough for digital cameras.
This technique is readily adaptable for all plaster dressing requirements including blending of plaster joints and/or repairs. I’ll get that up as soon as I can.
NOTE It’s a good idea to vary the angle while dressing because this gives the stone the random chiseled look.
Pick and Flick
Yes, it sounds like you are doing something else, but you’ll be simply picking a bubble and flicking the cast plaster around the bubble hole. In most cases you place the #11 blade next to the bubble then twist it a small amount, which tends to break and flick a a small chunk of the casting taking the bubble away with it. Sometimes it doesn’t remove the bubble completely, but you can either scratch at it with a small wire brush that will help blend it in with the adjacent stone texture, or in extreme cases can be built up with a small amount of plaster and made to blend with a tooth brush and a bit of the chatter technique.
Word of warning, using the Chatter and the Pick and Flick techniques make tiny chips that go everywhere. However, no where near the amount of dust a handpiece (Dremel) will produce. (I get more into that later). Also, most of the time you are drawing the knife towards you making all of the chips fly at you then onto the floor and onto anything that is within a 3 ft (meter) radius. I have a dust collector intake made out of couple of ABS plastic pipe fittings that comes up from below my carving workbench that connect to my shop vac system. This pipe points away from me and towards the work-piece, so as I pick and flick and chatter the chips fly into the vacuum. If you don’t want to do that you can always set up a jewelers apron that attaches to the front of the workbench and has a loop of string to go over your head. These aprons are also great for at the bench modeling as they help keep tiny flying parts from getting too far away.
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