OSMALTO - A background with history worth repeating.
Osmalto, or smalt for short, has a technical definition of bein crushed of powdered glass enamel, primarily blue, and has its roots in the jewelry trade. In Cloisonne work it was applied to surface designs sectioned off by thin strips of metaland fired in a kiln until melted. You often see small trinket boxes decorated in this manner.
The popular use in our trade began in the mid 1870's, coinciding with the birth of carved, wooden letters. For maximum durability and visibility, these letters were without a doubt, gold leafed and projected their own elegance.
Requiring a worthy background; it helps to understand the nature and practice of sign construction during this era: Plywood wasn't yet invented, so if the customer desired a mid-range sign, you nailed up wooden framework and covered it with a tin face. This gave a smooth working surface and required a minimum amount of effort. For the highest quality and weather resistant sign boards, wooden planks were doweled together. And to prevent any seams or cracks from ever showing, duck canvas varnish was affixed to the face. After initial sealing and priming, it would be wasted effort to build up its rough texture. And if accomplished, wouldn't appear any nicer than its cheaper, tin covered counterpart. There was considerable cost involved in hand carved and gilded letters so longevity was the main factor. The use of colored glass smallt was a natural conclusion. It not only disguised the rough canvas with minimum effort, but it imparted an elegant, glassy texture with durability and fade resistance bar none. I have seen existing exterior examples on the East Coast still attractive over a century of use. Longevity aside, it's a simple solution to the coarse or boring. The era of beautifully grained, sandblased, wood signs seems to be giving way to prismatic letter faced, computer routed urethane panels with perfectly smooth backgrounds just screaming for attention.
Smalt is divided into two categories: glass and sand. The latter is simply a beach variety traditionally coated with japan colors, (see Atkinson's Sign Painting or Gold Leaf Techniques, 4th Edition.) It has a nice dull to satin sheen to it, but because of it's paint finish, is best reserved for interior use. Although not readily available in its original supplied form, there is an extremely durible epoxy coated version manufactured by the Clifford W. Estes Co. of Lyndhurst, NJ, (an original maker of smalts in the last century), referred to as masonry aggregate and available in many colors.
The most commonly used is glass, for its shiny appearance and light fastness in exterior use. The most widely used is of the coffee ground size and comes in a range of colors: from jet black and ruby red to cobalt blue and dark green. Being almost always used with gilded graphics, the darkest colors are preferred for maximum contrast.
In order to attach the smalts to a surface, a smalt paint is required, although many materials have been used in recent years with varied results, (keep in mind that merey sticking them to the surface will give you bald spots with just short service.) They must sink into the adhesive a third to one half of their thickness to be permanently adhered. There is also the matter of open time when dealing with larger signs. The original recipe was to take a keg of white lead, (which was of paste thickness), break it down with additional linseed oil to a burshing cosistency and add some color to it to closely match the smalt.
In keeping with it's character, our modern method is to use a half and half mix of lettering enamel, matching the smalt, and a conditioning cream made for bulletin board pictorial work. Smith's Cream, Jack's Cream and Jones Cream are the brands that are available. Mixing the enamel and the cream together, 50/50, will give you the viscosity needed to affix the smalt, and allows sufficient open time needed to easily do a twenty foot sign with it's drying time: just overnight. Some craftsmen use a product called Hol-Fast oil or epoxies for small areas, but I'm assured open time is minimal.
For application, first prepare a smalting can by taking a coffee container and perforating the bottom overall with 1/8" holes using an awl or hammer and nail. Cover the bottom with a piece of pasteboard and fill the can. When the board is removed, you are able to evenly shake and distribute the smalt. This type of background isn't limited to raised letters or routed recesses, but is just as handsome with flat surface gilded inscriptions. Lay your panel flat on a horizontal bench or saw horse. With recessed or flat gilded work, apply the paint/cream mixture thickly, brushing from dry to wet until evenly covered. On larger or very long panels, you can paint in a certain distance, say a third of the area or so, apply the smalt heavily and evenly with 8"-10" of the wet end and continue with the paint where you left off. Your own judgement will dictate how much you do at once. As a rough rule of thumb, one pound of smalt will cover two square feet of area. You needn't wait until you've completely covered the sign with smalt before you dump off the excess. If you are running short on smalt, periodically flip the panel over rapidly with a tarp on the floor. This will catch the excess and allow you to reuse.
- Rick Glawson