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Past Articles from Glass on Metal

Experimental Techniques for Carefree Lusters
by Harry McDaniel
from Volume 13, Number 6, December 1994

     The December 1992 issue of Glass on Metal magazine includes an article on 'Lusters, A History of Dynamic Limitations' with a description of the new mica-based luster pigments stabilized for glass, glazed ceramic, and enameled metal applications.  These new lusters are now available to artists for one-of-a-kind pieces, exclusively from Thompson Enamel, under the name Carefree Lusters.  U.S. Patent No. 5,366,736 has been granted for this invention.

Photo 1     The November 3rd meeting of the Ohio Valley Enameling Guild hosted a lecture, demonstration, and hands-on workshop with Carefree Lusters by Harry McDaniel.  Most everyone in attendance found the lusters easy to use with cost, safety, and durability superior to the typical precious metal resinate luster.  Carefree Lusters are currently available in seven rainbow colors:  metallic yellow, orange, red; and clear silver, purple, blue and green.  These lusters are very similar in form and properties to the natural lusters found in pearls, peacock feathers, scarab beetles, and many butterfly wings.  The primary difference is that the natural lusters are organic, while Carefree Lusters are inorganic.

     The new lusters are supplied as fine powders (particle size 10 to 60 microns) which can be dusted dry onto a wet vitreous surface or dispersed in a gum solution (e.g. Klyr Fire or hairspray concentrate) for application by brush.  A concentration of less than about 10% by weight (30 to 40% by volume) is recommended for most liquid dispersions, including those for air brush and screen printing.  If a thinner dispersion is needed for air brushing, thin with a water soluble volatile solvent like isopropyl alcohol.  If a thicker one is needed for screen printing, thicken with an ashless organic solid like 200 to 325 mesh black walnut shells.  The lusters are essentially non-toxic, with similar materials finding use in women's cosmetics and children's toothpastes.  The material safety data sheets for Carefree Lusters list a chemical composition of mica flakes, and titanium dioxide and/or iron oxide.  Care, however, should be taken in handling the dry powders not to breathe the dust.

     Less than about one gram of luster per square foot colors the entire surface of an art object.  Using less, or underfiring the piece with an excess of pigment, will give a glossy finish, while the typical finish will be matt.  Varying the application thickness of the luster by dilution with solvent, will give an effect like watercolors not achievable with the precious metal resinate lusters.  Carefree Lusters when applied give close to the same appearance as after firing.  However, if the lusters are applied in excess, the excess will not bond to the vitreous surface and will rub/wash off.  For any given vitreous surface and at any given firing temperature/time, only a given amount of luster, and no more, will bond to the surface.  This bond is quite durable.  The bonded lustrous coating cannot be removed by dishwashing, acid, and/or non-abrasive scrubbing.  However, if the vitreous surface is scrateched, so will the durable lustrous coating.

Photo 2     Once the lusters have been applied wet to the vitreous surface in the intended design and allowed to dry, sgrafitto details can be scratched into the unfired coatings.  Hair spray concentrate, because of the hardness of its dried surface, is the recommended dispersing medium.  Dry under infrared lamps before sgrafitto details or firing of the enameled metal object.  For most enameled copper, steel and precious metal objects, a firing temperature of about 1200 degrees F to about 1300 degrees F for two to five minutes is recommended.  For enameled aluminum, a firing temperature of about 1080 degrees F for three minutes should be adequate.  Firing temperature is determined by the softening point of the underlying enamel.  The lower softening point enamels will require the lower firing temperature; and the higher softening point, the higher ones.  The side of the enameled object with the luster application can be facing down rather than up during the firing process without any loss in quality.  A Q-Tip rub off test of the lustrous coating after the object has been fired and cooled, can be made on a small portion of the design to assure bonding of the luster.  If the luster has not bonded to the degree intended, the cooled object can be returned to the oven at a higher temperature and/or longer time to assure bonding of the luster to the intended level.  Once the luster has been bonded, wash the cooled enameled object with water and detergent with non-abrasive scrubbing to remove any unfixed luster; then rinse and dry.  A Sparex or 10% nitric acid bath can follow to remove fire scale, with no damage in the durable lustrous coating.

     The durable lustrous coating in on the vitreous surface of the object with more or less transparency depending upon the thickness of the coating (more transparency for thinner, less for thicker coatings) and the type of luster (more transparent for clear, less for metallic lusters).  Since the lusters are transparent with more color and luster when the light is at the reflective angle to the lustrous coating, the color of the luster will be more apparent when the color of the underlying enamel is black or some other dark color.  With transparent enamels and visible underlying metal or metallic foil surfaces, the metallic luster surface coatings can and will provide a contrast and interplay with the underlying metal surfaces.

     These same lusters can be used on glass and on glazed ceramic objects, as well as on enameled metal objects.  The application techniques are similar but the firing times and temperatures will differ.  For float process flat glass, use the non-tin side for the luster application and fire at a fusing/slumping temperature of about 1380 degrees F to about 1480 degrees F in a temperature programmed cycle.  For glazed ceramics, a bisque firing temperature of about 1720 degrees F to about 1820 degrees F in a temperature programmed cycle will be adequate for most high fire glazes.  Glass and ceramic objects with Carefree Lusters are microwaveable, unlike those with precious metal resinate lusters.  The overlayer of the transparent glass as well as a flowing surface of water on objects with Carefree Lusters enhances their luster intensity.

     Gas fired as well as electric ovens are useable, but in both cases, avoid breathing of the dry lusters or collections of the lusters on hot gas jets or electric filaments.  The clear lusters decompose at temperatures of about 2000 degrees F.  At these temperatures, the opaque white titanium dioxide decomposition product may give cloudy stains on the surfaces of your vitreous objects.

Photo 3     Carefree Lusters are currently available in only seven colors/tonalities, but other lusters will become available as demand dictates.  Smaller ( 5 to 25 microns) and larger particle sizes (10 to 125 microns) will become available in most of the current seven colors/tonalities for a matt (smaller particle size) and sparkle finish (larger size).  Other clear colors (i.e. yellow, orange, red) can be made available on special order.  More importantly, become better acquainted with the current seven colors/tonalities already available.  You will need this experience before you can evaluate the other lusters.  The other lusters will follow closely the same application and firing procedures, but will deliver relatively non-dramatic differences in the end results of color and luster quality.

     Blending of lusters with other luster colors is not recommended because of the usual accompanying loss in luster intensity.  However, some lusters can be blended with unexpected, positive results.  Two parts of clear blue and one part metallic red gives a purple luster with more depth and opacity than the current clear purple, with no apparent loss in luster intensity.  More importantly, Carefree Lusters should not, and need not, be blended with transparent or opaque vitreous fluxes or frits to provide a durable lustrous coating.  Their addition results in a dramatic loss in lustrous quality as well as an excessive use of luster pigments.  Blends of luster pigments with vitreous fluxes and frits are covered by U.S. Patents No. 4,353,991, assigned to the Ferro Corporation.  Glass on Metal Magazine

 

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