Scrapers and Scratch Stocks

Some wood scrapers. Bottom is a hand held scraper, which is held to the wood at a slight angle, away, and with the thumbs pushing slightly in the center, to bow the scraper. Middle right is a scraper, that does all of the angling and bowing for you. Top is a stencil scraper, designed for removing stenciled shipping labels from wooden shipping boxes.

Most wood scrapers are "sharpened" in an unusual method; they are flattened on edge with a fine file, and perpendicular to the sides. Then, a burnishing tool is applied to that edge, flat and then with a very slight angle on each side of the working edge, bending the edge into a "burr". The burnishing tool is a polished and hardened rod or oval, fitted with a handle, to add the burr.

The "burr", that does the actual cutting, as seen above. Note that objects in drawing appear larger than they actually are. The stencil scraper, has however, just a conventionally sharpened edge, and the bow is already in the cutter, so that raising the handle narrows the cutting edge.

Some other methods of scraping wood include using broken glass as the tool, or razor blades, and even sharp knives can scrape the surface when held perpendicular to the work, or slightly angled. The wood is removed as shavings, much as if a plane was used.

The scratch stock is probably very ancient, as a tool, and is exceptionally versatile . If I need only a few feet of molding, I can grind a new cutter in minutes, sharpen, and be cutting wood very quickly.

My scratch stock, with a few of it's cutters, and the small, round file used for the sharpening. I've recently added an additional fence, to increase stability.

The added fence has increased control, and reduced the "ripple" effect common to working with a scratch stock. The ripple is caused by alternating bands of hard and soft wood. Light pressure on the cutter with heavy pressure on the fence will control ripple, and gesso and sanding reconciles a multitude of sins.


Scratch stocks, here, here, are sharpened in a similar way to the regular scraper. I sharpen my cutters by using the small round file, at a slight angle away from the cutter. A few strokes, on both sides, produces a "burr" that shaves the wood.

The Lazy Heretics Guide to Gesso

 Frame in White (Gesso)

(Edited several times)

The heretic comes from my "unusual" techniques and statements, and I also don't take my recipes and methods quite as seriously as some, but I'm involved with hide glues daily as a part of my profession, and I have been around for awhile. Lazy, too, so lazy that I often work very hard at trying to avoid work. Cennini was an obsessive-compulsive, whose recipes are incredibly over wrought, by the way. Heresy.

Everybody has a different recipe for gesso, and I think I've read them all, they all vary, so ultimately you have to make your own way. Ratios are, to me weird, because glue is a dry product measured by weight, and water is by volume. Ratio?  Also, there are different strengths of glue. The designation, RSG, is not rabbit skin glue, but hide glue, of a high strength. (Here's a ratio: rabbits to beef ... ) This is not particularly important because you need to do this by feel. Recipes are a starting point, and like some of the best cooking, subject to modification.

Start with 40-60 grams by weight of your dry glue material, to 20 ounces of water by volume. Soak, (length of soak depends on the granule size, or if you are using leaf or sheet glue. It needs to be wet, completely.) heat to 140-150 degrees, and then allow to gel, and cool. It should be a gelled material, firm enough to push with a finger, but soft enough that it can be fissured by pressing two fingers on to the gel and spreading them. Adjust your mixture to achieve that. Add whiting, French chalk, precipitated calcium carbonate, whatever. For a 20 oz. mix, I use 2 of the small tuna cans of precipitated calcium carbonate, by volume. (Very scientific, ehh?) The PCC is very even in texture, and is the same chemistry as chalk, etc. I usually let my mix sit, for at least a day, refrigerated if it is hot. This allows the PCC to absorb the liquid, and everything smooths out. My first coat is this mix, brush scrubbed into the surface, and licked off, so there is no real surface coating; very thin. It is absorbed into the surface of the wood.  Then I spray subsequent coats. Part of the reason for using my gesso mix as the sizing coat, is I can very clearly see that I have coverage, and I'm lazy. Once one has a feel for the mixture, it can be adjusted for different batches of glue, and for different properties, such as how hard it is to sand and carve. For frames, that require hand chasing and sanding I tend to a softer gesso. For panels, where I can use a power sander, a little harder is fine.

I also mix and heat my gesso in quart type canning jars, using a small microwave to heat the mixture. I use a quick read thermometer to learn how much time and at what power level on the microwave, aiming for 140 - 150 degrees. (electric glue pots, heating glue all day long, are set for approximately 150 degrees, and whatever you call it, it's hide glue, same stuff chemically)

Temperature is a touchy subject, some saying heating a mix to 140-150 degrees will ruin the mix, or when it touches the cooler surface of the substrate, will create pinholes. Actually, by the time it gets from the container, on the brush, and to the application, it has cooled considerably. I think pinholes come from not doing the first coat scrubbed and then "licked" off, vigorously. Licking it off is the important part. Spraying, even hot gesso, is cool by the time it reaches the substrate.

Additives: Uniodized ( I don't know that the iodine would matter, but it's that lazy thing) table salt can be added as a gel suppressant, to retard the setting of the gesso, letting air bubbles rise and escape, and also leveling the surface. Other gel suppressants are urea, used to make liquid hide glue, and large mammal urine. This is why some ancient recipes call for urinating in the mix on a dark and stormy night under an old oak tree. I'll just use salt, about a tablespoon (the palm of my hand) for my 20 ounce mix. I also add a "splash" of alcohol to the mix as a wetting agent, and sometimes to the framer, as a calming agent. This probably helps with pinholes, and helps the framer stop gyrating. I have some quart cans of solvents with squirt nozzles on them, so I'll count to 10 as I'm adding alcohol to the 20 oz. mix. Very scientific.

As with the salt, plain, I will often use distilled water, especially for bole, or filtered water for gesso. This falls under the heading of "materials safety", in that I eliminate things that might cause problems, such as all the additives in tap water, the iodine, etc..

So there, the lazy heretics guide to gesso.

An earlier post about pinholes.

Labels

Richard Christie, Evesham, Worcestershire, United Kingdom, has been posting a lot of interesting labels over on the label blog.