Cristallo
Encyclopedia
Cristallo is a glass
which is totally clear (like rock crystal), without the slight yellow or greenish color originating from iron oxide
impurities. This effect is achieved through small additions of manganese oxide
. Often Cristallo has a low lime
content which makes it prone to glass corrosion (otherwise known as glass disease
).
The invention of Cristallo glass is attributed to Angelo Barovier around 1450.
Materials
In addition to common glass making materials manganese, quartz pebbles, and alume catino is used in the making of cristallo glass.
Rather than using common sand crushed quartz pebbles were used instead. The quartz pebbles were typically from the Ticino and the Adige rivers. The quartz pebbles went through a rigorous screening process before being selected for use in cristallo production. The quartz pebbles had to be free of yellow and black veins and also had to be able to produce sparks when struck with steel.
If the quartz pebbles passed the selection process then the pebbles were heated to the point where the stones began to glow and then paced into cold water. Then the pebbles were crushed and ground.
The typical flux was used in the production of cristallo was called alume catino. Alume catino was derived from the ash of the salsola soda and salsola kali bushes that grew in the Levantine costal region.
The ash of the plants was then carefully sieved and then placed into water to be gently boiled with constant mixing. Then the ashen mixture was placed into shallow pans to be dried. Once dried the alume catino would repeat the boiling and drying process until all of the salt was extracted from the ashes.
Process
The crushed and ground quartz was mixed with the purified alume catino and constantly mixed at high temperatures until. Then the top of the molten batch would be skimmed off. By skimming the top off the molten glass unreacted and undissolved chlorides and sulfates in the mixture was removed.
Then the molten glass would be ladled into vats of water. The water removed chloride and sulfate impurities from the mixture. The process of remelting and placing the molten mixture into vats of water was repeated several times until the glassmakers were satisfied.
Next the glass was placed into furnace that was heated to the highest temperature possible and left there for several days. The material was stirred continually to eliminate defects, such as bubbles.
Then the refined mixture was taken and heated and shaped into blocks called frit. The frit is then taken and remelted. Once the frit is melted the batch is skimmed once again in order to remove impurities and had manganese added to the mixture at this time. The addition of manganese helps to rid the cristallo of any color tints. This step is repeated until the glassmaker is satisfied.
Now the molten mixture is ready to be shaped by glassmakers into pieces of cristalloware.
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
which is totally clear (like rock crystal), without the slight yellow or greenish color originating from iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
impurities. This effect is achieved through small additions of manganese oxide
Manganese oxide
Manganese oxide is a generic term used to describe a variety of manganese oxides and hydroxides. It may refer to:* Manganese oxide, MnO* Manganese oxide, Mn3O4* Manganese oxide, Mn2O3* Manganese dioxide, , MnO2...
. Often Cristallo has a low lime
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
content which makes it prone to glass corrosion (otherwise known as glass disease
Glass disease
Glass disease, also known as sick glass, is a degradation process encountered in art conservation.Glass disease is caused by an inherent fault in the chemical composition of the original glass formula. Usually, inadequate calcium oxide causes the alkalis in the glass to remain water soluble at a...
).
The invention of Cristallo glass is attributed to Angelo Barovier around 1450.
Materials
In addition to common glass making materials manganese, quartz pebbles, and alume catino is used in the making of cristallo glass.
Rather than using common sand crushed quartz pebbles were used instead. The quartz pebbles were typically from the Ticino and the Adige rivers. The quartz pebbles went through a rigorous screening process before being selected for use in cristallo production. The quartz pebbles had to be free of yellow and black veins and also had to be able to produce sparks when struck with steel.
If the quartz pebbles passed the selection process then the pebbles were heated to the point where the stones began to glow and then paced into cold water. Then the pebbles were crushed and ground.
The typical flux was used in the production of cristallo was called alume catino. Alume catino was derived from the ash of the salsola soda and salsola kali bushes that grew in the Levantine costal region.
The ash of the plants was then carefully sieved and then placed into water to be gently boiled with constant mixing. Then the ashen mixture was placed into shallow pans to be dried. Once dried the alume catino would repeat the boiling and drying process until all of the salt was extracted from the ashes.
Process
The crushed and ground quartz was mixed with the purified alume catino and constantly mixed at high temperatures until. Then the top of the molten batch would be skimmed off. By skimming the top off the molten glass unreacted and undissolved chlorides and sulfates in the mixture was removed.
Then the molten glass would be ladled into vats of water. The water removed chloride and sulfate impurities from the mixture. The process of remelting and placing the molten mixture into vats of water was repeated several times until the glassmakers were satisfied.
Next the glass was placed into furnace that was heated to the highest temperature possible and left there for several days. The material was stirred continually to eliminate defects, such as bubbles.
Then the refined mixture was taken and heated and shaped into blocks called frit. The frit is then taken and remelted. Once the frit is melted the batch is skimmed once again in order to remove impurities and had manganese added to the mixture at this time. The addition of manganese helps to rid the cristallo of any color tints. This step is repeated until the glassmaker is satisfied.
Now the molten mixture is ready to be shaped by glassmakers into pieces of cristalloware.