Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1997-06-03
2001-07-10
Reddick, Judy M. (Department: 1713)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S391000, C427S393000, C427S393500, C427S411000, C427S412100, C427S419600, C427S420000, C430S322000
Reexamination Certificate
active
06258412
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This present invention is directed in general to a composition and methods of manufacture of artistic media and, more particularly, to a composition and methods of manufacture for clay-surfaced substrates.
BACKGROUND OF THE INVENTION
The use of clay as a medium for drawing or painting is not new. Countless millennia before mankind developed the ability to communicate in written or spoken language, drawings, in the form of petroglyphs, were used to express ideas and concepts. Unfortunately, these drawings required large quantities of rock face or clay and were not portable. Also, erasure was a major problem.
To answer these deficiencies, canvas came into use several hundred years ago, allowing the artist to paint pictures on lightweight, portable media. However, changing or erasing the painting once dry was difficult to nearly impossible, the canvas aged and rotted and had few of the stabilizing and texturing qualities attributable to clay.
In an effort to marry the desirable surface qualities of clay or other rock with the light weight and portability of canvas, the prior art has provided an artistic medium termed “scratchboard” or “scraper board.” U.S. Pat. No. 2,523,650, which issued on Sep. 26, 1950, to Dickson, is representative of such prior art and is directed to scraper and process boards capable of being engraved or carved. Dickson teaches deposition of a relatively thick layer of china clay and a bonding agent (water-soluble hide glue) over a comparatively rigid backing, such as paste-board, ply-board or sheet metal. Deposition is by spraying.
Unfortunately, the scraper board disclosed in Dickson suffers significant shortcomings. First, the scraper board lacks the desired degree of permanence in several respects. First, the surface is non-permanent in the respect that the binder provided is optimized to bind the clay to the board and not the clay to itself. Therefore, the clay can erode as it is worked. Second, since the thin clay layer is relatively inflexible, it tends to crack easily when the relatively flexible cardboard is bent. This, too, is related to the strength of the binder.
Third, artists not working just for reproduction purposes often wish to fix a completed work on an inflexible substrate for more permanent display or storage, a necessity with fine art. Unfortunately, the cardboard backing of Dickson is not amenable to such mounting. If water-base glues are used to bind the cardboard to the inflexible substrate, the glue is liable to soak through to the clay layer, dissolving the gelatin glue and creating visible imperfections. If rubber cement is used instead, its hold may be released over time causing the formation of large bubbles in the scraperboard, thus ruining its mounting.
Fourth, since the binder of Dickson is water-soluble, it looses its integrity when wet, causing the dry clay surface to loose its binding strength and soften when wet, causing the clay surface to disintegrate when subjected to water. As such, the clay surface is limited for some watermedia techniques and photographic printing which requires total immersion of the media in water.
Fifth, the manufacturing process taught in Dickson (spraying of the clay onto the cardboard) limits the maximum size of the scraper board to about 20×30 inches, thereby limiting the opportunity of an artist to create larger scale work using the “scratchboard” technique.
Sixth, manipulation and reworking of the drawing or painting are limited due to the comparatively thin layer of clay on the soft cardboard base.
Seventh, cardboard-backed scratchboards have a tendency to crack when bent in a curve of at most 12 inches in diameter in a dry environment, e.g., approximately 10% relative humidity. This is an absolute requirement drum-type laser printers, representing the state of the art for illustration reproduction.
Eighth, the surface of the Dickson board is pitted due to small bubbles formed in the spraying application of the wet clay. These pits become obvious defects in the drawing and painting processes and contribute to the structural unsoundness of the surface.
Ninth, the manufacturing process does not lend itself to cost-effective mass production. Several spray coats of clay must be applied to each board to achieve suitable clay thickness. This results in significant manufacturing time and labor requirements.
The clay surface of Dickson allows minimal artistic manipulation. When drawing, the surface indents too easily when a sharp pencil is used, making it difficult to manipulate the line with subsequent scratching or abrading techniques. If bubbles are within the clay coating, manipulation can expose those bubbles, thus creating more surface pits.
Finally, spraying of the unrefined clay coating of Dickson onto the cardboard backing typically produces a fine mist of clay dust, containing silicates and quartz particles. Prolonged exposure to clay dust created during manufacture or artistic use can cause silicosis due to the presence of quartz crystal impurities in the unrefined clay.
Another scratchboard is disclosed in U.S. Pat. No. 1,923,483, which issued on Dec. 7, 1927, to Glenn. Glenn teaches use of a backing sheet in the form of a dense, pressed paper board (sold under the brand names “Vehisote” or “Masonite”) upon which is deposited a shellac and a layer of mineral earth (principally magnesium silicate) in the form of purified talcum powder mixed with water into a paste. Deposition is performed by heaping a mass of the paste onto the backing sheet and jogging the backing sheet until the paste covers substantially all of the sheet.
Although Glenn provides a shellac and a hard backing to overcome some of the above-noted problems, Glenn fails to provide for the flexibility required for the board to run through a laser printer. Additionally, the jogging deposition method of Glenn is slow and tedious and can still cause bubbles to become entrained in the coating. Finally, Glenn fails to provide a water-resistant binder to securely fix the paste to the shellac when the dry coating is subjected to application of water.
Finally, the prior art provided a scratchboard that consists of a clay surface composed of “6 tile Georgia kaolin” clay bound together and to a ⅛ inch hardboard backing (again, Masonite) with a dilute adhesive. The permanence and physical durability was greatly increased by the clay being applied to a rigid flat base (a hardboard), a factor which also solved the mounting as described above. The board was frame-ready, and needs no glass for protection when sealed with an acrylic or varnish sealer. Provision of the rigid base and the dilute adhesive binder allowed the surface size to be extended up to 4 feet by 8 feet. This prior art scratchboard also provided a thicker clay layer, allowing more vigorous manipulation and reworking. Use of the dilute adhesive binder in the clay mix also gave much better water resistance, thus allowing the use of waterbased painting on the scratchboard.
The 6 tile kaolin scratchboard thus solved most of the above-noted problems with the earlier forms of scratchboard, but created in their place some new ones. First, the manufacturing process, never developed for mass production, was similar to that taught in Dickson, i.e., multiple spray coatings. This process was time and labor intensive, and, more important, produces small bubbles (on the order of 0.004-0.015 inches in diameter) that dry in the clay layer, becoming unwanted surface pits in the drawing, painting, and photographic print surface or, more insidiously, latent defects within the clay coating itself, becoming exposed only as the artist works. Manufacturing of 6 kaolin scratchboard required extensive refinishing to minimize the number of bubbles, resulting in considerable loss on material to the air and creating a risk of silicosis to workers exposed to atomized clay mist containing quartz particles.
The spraying process employed in producing the prior art 6 tile kaolin scratchboard, coupled with the need to layer the applications, made production
Head Johnson and Kachigian
Reddick Judy M.
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