tehnicĂ Şi artĂ În articolele decorative din sticlĂ stratificatĂ

7/25/2019 TEHNIC I ART N ARTICOLELE DECORATIVE DIN STICL STRATIFICAT

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2015 NUMBER 12 JIDEG

Abstract: This paper presents the way technique and art combine to create laminated glass items,

particularly laminated glassware engraved with acids, with reference to artistic reproductions from the ArtNouveau period, Gall, Daum-Nancy, items with metallic coating such as bronze, brass etc. The paper will

highlight aspects concerning glass characteristics, glassblowing methods, techniques of acid engraving,the art of decoration and the technology of mounting auxiliary metallic components.

Key words: laminated glass, chemical engraving, design, art, Gall, Daum-Nancy.

1. INTRODUCTION

Artistic processing of laminated glassware dates backto the discovery of the "Portland vase", recorded as seenin 1601 in cardinal delMonte's collection, in

Italy and theneventually arriving inEngland to the Portlandfamily from whom theBritish Museum boughtit in 1945 [1]. The baseglass is blue, coveredby a second layer ofmilky white glass,artistically molded inembossed mythologicalsigns, figure 1.

From that momenton, thousands of similarmodels were created,standing out mostly during Art Nouveau, Gall, Daum-Nancy, Mller, Schneider, Lalique etc., figures 25 [3],[4], [5], [6].

Fig. 2 mile Gall vase [3] Fig. 3 Daum-Nancy vase [4]

Fig. 4 Schneidervase [4]

Fig. 5 Mllervase [5]

Fig. 6 Laliquevase [6]

The moment glass was invented and until thediscovery of glassblowing technique, the progressobtained by creating decorative artifacts made of glasswere significant. Decoration can generally be summed upby 2 methods: decoration under heat, vase modelingbeing done in wooden or metal mold (aluminium, mold

iron, steel, heat resisting steel). During the blowingprocess, molten colored glass layers are added to the baseglass. The second method is decoration at a coldtemperature, manually or with a wheel by bevelling orengraving [7]. A distinct technique is that of a falsecameo, obtained by applying two or more layers of glass,the decoration resulting from modeling the externallayer. Usually, the artistic image is placed on acontrasting background, on a colorless base covered witha colored translucid layer or, like in the case of laminatedglass, with layers of different colors [8]. Pigments arefrequently used to enhance these colors.

At the same time, the decoration can be done byblowing powder and particles of colored glass, through

metal coating with bronze and brass, incorporating theglass into metallic mold etc. The technology to createdecorative items from laminated glass entails, in fact,creating a glass bas-relief, on which you can applytechniques such as engraving or other specific types ofchemical treatments. For these, it is necessary to haveknowledge about glass and furnaces' characteristics, themelting temperature points, the blowing style, pigmentsused, and last but not least, the creator's artistic vision.

Nicuor BAROIU, Mihaela PETREAN, Elena Felicia BEZNEA

THE ART AND TECHNIQUE OF DECORATIVE ARTIFACTS

MADE FROM LAMINATED GLASS

Fig. 1 Portland vase replica [2]


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Tehnici artn articolele decorative din sticlstratificat


2. GLASS CHARACTERISTICS

Despite the fact that, usually, one of the mainrequirement for glass is to be durable against chemicalreagents such as acids and alkali, the artistic processingof laminated glass is done by keeping in mind that exactrequirement, and also the favorable chemical andphysical properties they offer. That is why glass, as amixture made up from silica and complex silicate of Na,K, Ca, and Pb, by fast cooling it turns from a liquid state(glass melt) into a solid amorphous state.

In table 1, you can see the main mechanic propertiesfor glass used in creating laminated decorative artifacts.

Table 1 Mechanic properties of glassResistance to

compression

Resistance to

bendingDensity

1000 MPa 120-200 MPa 2500 kg / m3

Elasticity

modulus (E)

Poisson ratio

()

Hardness on

Mohs scale

70 GPa 0,22 6

Because of low thermal conductivity, the alternatingcooling and heating of glass lead to tensions that cancreate heat shocks. For this, a special emphasis is placedon thermal resistance of glass, defined by the linear heatexpansion factor - extension on a unit of length for avariation of 1 0C. For glass, this factor is low, 9 . 10-6.

Heat resistance of glass containers depends on theirshape and type of glass, containers with a flat bottombeing less durable when heated than those with a roundbottom or cone-shaped ones.

3. THE FURNACE AND GLASSBLOWINGTECHNIQUES

After creating the mix of silica sand, soda, and chalk,to which defining factors contribute, such as structure,color, and style, it must be molten at high temperatures,in special furnaces.

The base material used, chalk glass, transparent oropaque, is molten at temperatures above the 1500 0Cvalue and at a pressure of over 30 bars.

In this study case, the melting point temperature ofthe glass is 1450 0C, and its processing temperature is1100 0C. Once the glass melts, CO2emissions take place,which homogenizes the melt and stirs the glass. Theglass melt shifts to the other end of the furnace, slowlyrising to 900-1000 0C. and increasing its tackiness, thus it

can be turned into different objects, modeled.When modeled, the melt abruptly cools down from900-1000 0C to 20-25 0C, which leads to an irregularcooling inside the glass matter and internal stress. Thisstress is released by recalescence - re-heating the newproducts at temperatures of 500-600 0C and slowingcooling them.

The furnace used for melting Falorni type glass - MG350 EL GAS FIRED, figure 7.

The main characteristicsare the small size design,completely automatedcombustion system, withfull control overtemperature. It has aninterchangeable glasstank and a control panel,separated from thefurnace, for gas control,flame and temperature ofthe furnace, made from:1-antivibration joint; 2-gas filter; 3-pressure gauges; 4-pressure reducer; 5-gaspressure switch; 6-solenoid gas valves; 7-pneumaticbalances; 8-gas flow meter; 9-burner; 10-air valve; 11-melting furnace; 12-thermocouple; 13-hot recuperator;14-air pressure switch; 15-fan; 16-electronic frequencyinverter; 17-temperature regulator, figure 8.

Fig. 8 Falorni furnace control panel [9]

In table 2, you can find technical characteristics of theMG 350 EL GAS FIRED furnace.

Table 2 Technical characteristics for MG 350 furnaceMax melting temperature:

1450C

Electrical power installed:6 kW

Workable glass: 350 Kg Furnace weight: 2500 Kg

Glass Capacity: 450 Kg Tank Inner Size: 900 mm

Energy to maintain 1000C:8 Nm /h

Tank Glass Depth: 350 mm

Total GAS consumption 24hours: 310 Nm

External dimensions:1700 x 1700 x 100 H

Glassblowing is one of the best-known modelingtechniques. This is the process applied to shape glass,without using a mold, the glass having a molten, semi-

liquid state. Glassblowing involves a blowpipe made of ametal resistant to high temperatures (heat-resisting steel),preheated in the furnace, through which air is literallyblown and which the glassblower gathers the moltenglass from the furnace. The glass extends until it reachesthe shape of a balloon. Color or more glass is added,using appropriate tools that semi-liquid glass cannot burn(punties, wooden molds, tongs, shears etc.).

Blowing directly into the molds is also practicable.

Fig. 7 Falorni furnace [9]


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4. PIGMENTS AND MOLDS

Colored glass is obtained when metallic oxides (Fe,Co, Cr, Cu etc.) are added to the molten glass, whichcreates a colored silicate.

Colored glass, which is ordinarily found in the shapeof rods, is molten in crucibles of different capacity ofaround hundreds of liters, or in small furnaces(trumeres), in which the temperature and theenvironment can be rigorously controlled, figure 9.

The glass industry uses as pigments a large number ofsubstances that can be divided into three categories: ionicpigments, molecular pigments, and colloidal pigments.

Ionic pigments are generally metallic oxides. Forexample, red glass contains copper oxide, yellow glasscontains cadmium sulfate, blue glass contains cobaltoxide, green glass contains chromium oxide, purple glasscontains manganese oxide. Uranium trioxide gives ayellow-green color, with a beautiful green glow.

Molecular pigments are represented by selenium thatgives a pink shade, by sulfur that gives a yellow or

brown-yellow color, and especially by the sulfur andselenium compounds of different elements.

The CdS + CdSe synthesis is very popular, giving aruby-red color, whose shade depends on the ratiobetween the two components.

Colloidal pigments are actually metals which undergoproper thermal treatments and, as a result, they disperseas a colloidal liquid, giving glass colors that depend onthe size of colloidal particles.

For mass production, in the glassblowing processgraphite or metal mold are used. Their advantage is thatthey have high resistance. Plaster molds can also be used,but they are inconvenient because of residue andpainstaking processing.

Wooden molds are much cheaper and easier toproduce. They are usually made from a solid chunk ofwood. The inside shape is obtained by facing on awooden lathe, using cutting tools and special devicesmounted on the lathe. After clearing the residual woodinside the mold, it can be divided into two or more partswhile also drilling holes to eliminate air through themold's walls. With the help of a metal tube, a globe ofhot glass is inserted into the mold and is constantlyblown into so that the globe takes the desired shape,figure 10.

a b cFig. 10 Using the mold to create the shape of the container[10]: a wooden semi-molds; b inserting the glass globe

into the mold; c blowing the glass into the mold.

5. WORK METHOD

Although in most cases, consumer items, of massproduction (glasses, statues, vases etc.) are obtained bymechanic pressing or blowing, decorative items made oflaminated glass, unique and personalized, are not madewith completely automated processing systems,developed in the 20th century. Instead, they are purelymanually executed, the processing stage of blowing

taking place after melting.Thus, the main stages of creating a decorative artifact

made of glass are:

1.Melting the colored bars in the trumer, figure 11.Usually, each furnace is operated by several wellcoordinated members. The blowpipe that contains thecolored bar at one of its ends is inserted in the trumer andconstantly rotated, so that gathering the molten glass atthe end of the blowpipe is relatively even.

2. Obtaining the molten glass globeThe glassblowing process involves channelling air in

the molten glass at the end of the blowpipe, whose effectis to extend the semi-liquid glass into a small, elongated

balloon, as a first stage. Subsequently, the glass is shapedby being rolled on a wet, wooden stand so that it isshaped as round as possible, figure 12.

Fig. 12 Obtaining the glass globe [10]

3. 3. Adding the layers from the colored bars.Over the glass globe, molten layers from the colored

bar are added and while the glass is still hot, the ends arecut and flattened on a metallic stand, figure 13.

Fig. 13 Adding bars of colored glass [10]


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By simultaneous blowing, the process is repeateduntil the components of the new structure blend,obtaining a structure in the shape of a funnel, figure 14.

Fig. 14 Creating the glass funnel [10]

4. Modeling inside the mold

The glass is modelled and inserted in a previouslyshaped wooden mold, and by continuously blowing intoit, the container will take shape, together with thedecoration according to the inside surface of the mold seefigure 10. The most important step in the glassblowingprocess is the transfer, in which case the glass piece andthe blowpipe are separated, figure 15.

Fig. 15 Detaching the piece from the blowpipe [10]

5. Applying thermal treatment of re-heatingThe items obtained in the mold are removed and

inserted in the reheating furnace, where gradual coolingof the pieces is done, to prevent cracking caused byinternal stress. It is recommended to keep the items in thereheating furnace at least 28 hours until completecooling. The final color of the artistic glass artifact willbe revealed only after it is completely cooled down andremoved from the reheating furnace.

6. DECORATION

Finishing and decoration of the laminated glass itemsare procedures that aim to create surfaces withremarkable characteristics through polishing, engravingand painting. Multiple techniques of glass decoration, onflat or embossed surfaces, are well-known. Among these

we can mention: embossed decoration with lead ribbing a technique hard to apply, the lead used for ribdecoration being a toxic compound [11], metallic ribbingin reticular net, glued with an elastomeric adhesive [12],decorative mixtures that contain epoxide resins ofBisphenol A type [13], opaque cover of decorated glasswith an ink mixture, followed by drying the protectedlayer and engraving. The next step is to cover the glasswith another sheet of laminated glass and glued withadhesive [14].

Many methods have the disadvantage that theycannot be applied on curved surfaces, like in the case ofengraving with a mask image and a photosensitive film[15], transferring a digital image, point by point, withspecial colored ink or applying a painting by burning iton the cast glass.

To remove these inconveniences, the decorationcreated through processing of the exterior layer isobtained using substances that corrode glass, such ashydrofluoric acid or mixtures of chemical compounds.

Hydrofluoric acid strongly affects glass, a wateryliquid of acid with a 38,2 % concentration; it has aboiling point of 112 0C, this depending on theconcentration of the mixture.

In general, engraving glass is done with a mix thatcontains: 10 grams of NaF; 1,5 grams of NaCl; 1,5 gramsof sodium carbonate and 4 grams of hydrofluoric acid.

Layered compositions are used for decorating glassitems, made of paraffin, beeswax, carbon black, bitumenand colophony resistant to the effect of certain glasscorrosive liquids (hydrofluoric acid), covered by aphotosensitive layer. The two layers covered with theflexible plate containing the desired drawing are exposed

to light and are successively developed [16].One of the most spectacular processes of decoration

is still painting, in which the artist transfers onto glass hispersonal passions, in various designs and colors,harmoniously combined.

On the glass surface of the item, previously wipedwith industrial alcohol or diluted steel with 40% waterand, possibly, chemically spliced, a first graphicrepresentation or painting is created. On the outline ofthe drawing previously done, a ribbed paste is applied,after which it is dried at room temperature for 24 hoursor at 510-530 0C, for 2 hours and 30 minutes. The clearspaces among the ribs are colored with a mixture ofcolloidal paint, mineral pigments etc., figure 16.

The procedure is followed by dipping it in the acidmixture, resulting in differences in sections between thepainted glass layers and the clear ones, as a result ofchemical reaction.

a b c

d e f

Fig. 16 Decorating a laminated glass object [10]


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After finishing the decoration by painting andrepeated chemical exposure, the resulted product is left todry for 24 hours, at room temperature or at 510-530 0C,for 15-20 minutes. The final drying stage is followed byopen air drying for 2 hours.

Given that there is an array of decorative artefactsmade from laminated glass, these can be divided basedon the accessories applied to them as follows: artefactswithout metallic accessories, figures 1721 and artefactswith metallic accessories, respectively.

Fig. 17 Embossed vases [10]

Fig. 18 Small vases - 615 cm [10]

Fig. 19 Medium height vases - 2025 cm [10]

Fig. 20 Tall vases - 3045 cm [10]

Fig. 21 Candy bowls [10]

To create metallic mountings of bronze and brass forlamps, light fixtures, ceiling lamps, chandeliers, vases,glass holders etc., with different shapes, figure 22, weemploy mold pressing followed by processing the surfaceof metallic objects, which is done by cutting or plasticbending to obtain embossed ornaments or to finish offthe embossed surface.

Fig. 22 Bronze and brass accessories for decorative itemsmade from laminated glass [10]

Combining decorative laminated glass items andmetallic accessories accentuates finesse, sensitivity andartistic refinement for these works of art, figures 2325.

Fig. 23 Ceiling lamps [10]

Fig. 24 Lamps with metallic holder [10]


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Fig. 25 Lamps without metallic holder [10]

7. CONCLUSIONS

The present paper defines the stages of work in asimple way, in an attempt to transpose the art andtechnique through all their successive stages, from thefurnace to engraving.

Decorative artefacts made from laminated glass andobtained through the false cameo technique can representdifferent symbols transferred onto glass: plants, insects,geometric shapes etc., offering the viewer a show ofcraftsmanship, by overlapping color layers, throughsimplicity and confidence of chromatic texture.

8. REFERENCES

[1] Walker, S.,Portland Vase, London, British MuseumPress, 2004;[2] *** http://www.cmog.org/-Corning Museum of Glass;[3] *** http://www.tinyesveld.com/;[4] *** http://www.prices4antiques.com/;[5] *** http://www.christies.com/;

[6] *** http://fineart.ha.com/;[7] Bejan A., Micle D., Arheologia - o tiin

pluridisciplinar. Metode clasice i moderne de lucru,Ed. Excelsior Art, Timioara, 2006;

[8] Malcolm, F., Vintage beauty, The National TrustMagazine, 2008;[9] *** http://www.falorniglass.com/ - Falorniglass;[10] *** http://www.corpuriiluminattipgalle.ro - GraurStil Glass;[11] Patent nr. RO 116807 B1, Process for the decorationof glass and beading device. Authors: Manta D.M., CocaC., 2001;[12] Patent US 4619850 A, Decorative window productand process, Author: Charlton T.J., 1986;[13] Patent WO1999006336 A1, Glass decoratingcompositions using bisphenol A epoxies, Authors:Kamen M.E., Hu M., 1999;[14] Patent EP0686495 A1, Process for producinglaminated ornamental glass, Author: Lin C.H., 1994;[15] Patent EP0506959 A1, Method of engraving withimage mask and photosensitive laminate film for saidimage mask, Authors: Tsutomu H., Suzuki, I., Aza T.,Ishimakihonmachi S., 1992;

9. ACKNOWLEDGEMENT

The authors gratefully acknowledge the support of

the Neculae Graur - Manager SC Graur Stil Glass SRL,Doina Graur - Creative Director SC Graur Stil GlassSRL, and Eng. Adrian Cristian Petrean - TechnicalDirector and all SC Graur Stil Glass SRL Buzumembers and staff (http://www.corpuriiluminattipgalle.roTel.: +040238718937; E-mail: [email protected]@corpuriiluminattipgalle.ro).

Authors:Nicuor BAROIU, Assist. Prof., PhD., Department ofManufacturing Engineering, Dunrea de Jos Universityof Galai, Romnia, E-mail: [email protected] PETREAN, Head of Customer Department SCGraur Stil Glass SRL, Buzu, Romnia,

E-mail: [email protected] Felicia BEZNEA, Assoc. Prof., PhD., MechanicalEngineering Department, Dunrea de Jos University ofGalai, Romnia, E-mail: [email protected]

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