Besides glass- there are also stone bottles. Or actually stoneware bottles. These jars or stoops (Dutch word) are predominantly known as packing for gin. It therefore is possible to make without glass (based on sand) bottles of clay. The unified shape makes it clear that they are not thrown, but cast. But how does that work?
A stoop was also a measure of capacity of about 2.4 liters. In one stoop went two ‘mingel’ or 2½ can.
To make stoneware suitable (stoneware) clay is needed. Which can be found in the Rhine and Meuse region. Grès is the French word for stoneware, sometimes recognizable in the naming of tiles and vitrified clay pipes for sewers. Cologne was the most renowned production and distribution center. In addition, also Raeren, Frechen (and Maastricht) are known. Stoneware is designated by the name of the city or area in which it was manufactured.
From the color of the shard is sometimes seen the place of origin of the clay. Which is yellowish for the Meuse. Raeren, Frechen and Cologne stoneware have a dark gray paste while the salt glaze is evenly brown.
Stoneware bottles were originally thrown. Customers took their own neutral bottle, sold by itinerant German traders, back to the distillery. Other jars were used for mineral water, until in the middle of the 19th century everywhere waterworks were established.
Bols made the jugs world known. Between 1852 and 1879 they were made by hand and given a 'blind stamping' with the brand name. Thereafter, they were machined to 1914, followed by a hand-fixed traditional ear. Because this could not be done by machine, the ear disappeared completely in 1918.
Stoneware occurs around the last quarter of the 13th century. From the 16th century, one could control the heat in large ovens good enough. Firing took several days. It was day and night burning. The temperature should be at least 1250° Celsius.
Only in the 14th century stoneware was given a salt glaze. Salt evaporated at 1250°. So to test the temperature the potter sprinkled a little salt in the oven. Thereafter, the oven was "salted". For this one scattered (about 400 kg), salt (NaCl) through the openings of the oven.
This sodium chloride will change during the baking in sodium oxide and hydrochloric acid. This comes as a hydrochloric acid gas in white clouds out of the oven. The fumes strike down as sodium aluminum silicates. So the clay is sintering, after salt or soda has been added to the baking process. Soda from salt binds to silica from clay during the biggest heat.
On reduction fire the furnace will be closed at the proper temperature so that no oxygen will enter. The fire retrieves the oxygen it needs to burn than out of the stoneware, causing it to be even stronger. In addition also come unhealthy chlorine gas.
Salt Glaze is transparent, but coloring by additives.
Reduction firing until the end gives a gray tint. By allow fresh air at the end the pieces become brown.
The glazed and fried pitchers were suitable for liquor and even for sour lime juice that served on long sea voyages to prevent scurvy by a vitamin C deficiency.
The jars were stacked one on another in the oven. In order to avoid that they were fired together were between two layers small, sand-covered clay platelets placed. In Raeren they were called "Krätzchen". They could be used only once. Then they were recycled as floor tiles.
Approximately 30% of the content had burn marks, a failed glaze, was distorted or wrong discolored. Misfires arrived in the shards pits or in the walls of new furnaces.
The uniform production used plaster molds. A mold may be made by applying a (e.g. rotated) model in a wooden box. Fill that for 1/2nd with plaster (CaSO4.2H2O). Leave everywhere a solid edge of a few centimeters thick. The neck should be adjacent to the edge, as this is also the pouring opening. Extra space here can be useful as a reservoir from which is supplemented the by drying reducing mass. Use the model also to position the two parts of the mold well. Provide reliefs and recesses (knobs, and key- hole) to get both parts fit well together. You can thus create several identical molds. Taking into account the shrinkage, the model should be approximately 115% of the desired final shape.
As a plaster mold becomes clogged (sucks insufficient water from the clay) it can be cleaned with vinegar in water. Most of the molds can be used up to twice a day.
Engobe comes from French gober (swallow without chewing). Mud or clay slip is a viscous clay paste to apply a coating to dry (unfired) ceramic objects, or to adhere clay components (e.g. spout and ears in a teapot).
Casting clay is made with 350-400 grams of water per kilogram of dry clay mass. First an electrolyte is dissolved in the water, then the clay goes in. The electrolyte is an ion exchanging deflocculant as sodium carbonate (or soda) or sodium silicate (or water glass). (I will limit it here to traditional non-industrial products.) Without an electrolyte it would be difficult to pour pasta.
Too much electrolyte makes the clay unusable. Better follow a good known recipe for casting clay.
A clay particle has a negatively charged core and a positively charged outer layer which makes them stick together.
A deflocculant exchange ions with the clay particles so that electron bonds are broken and the particles repel each other and continue to slide over each other. So you get a lot of clay particles and sludge with little water.
The viscosity of the fluid may be determined by a Ford cup, a cup with a hole (4 mm) or a funnel with a small hole in which the time of deflation of a known volume is a measure of the viscosity.
Wet liquid clay with the consistency of milk shake can be poured into the mold. Cast preferably (through a sieve) along a wooden stem to the bottom, so that there are no splashing droplets drying too early higher on the wall. A little vibrating drives the air bubbles out. The plaster absorbes the liquid and thickens the clay like a smooth skin at the wall. Fill and add some molding clay when the level decreases because the plaster derives water of the clay. You may cut a little pouring edge off in order to check the thickness.
After 20 to 25 (sometimes up to 60!) minutes, the remaining clay sludge is poured out. (With porcelain clay already after 3 to 10 minutes.) Pour slowly, without ‘clucking’: this would suck air from inside and can distort the fragile shell.
The next day you can take the leather hard form out of the mold. First cut off the pouring edge. Due to the shrinkage during drying, the jar comes off the mold by itself. Then you can smooth and polish the outer edges and seams. (And possibly press a mark.) Then continue to dry to fire later.
The timing between filling and emptying determines the wall thickness (3-8mm). The drying in the mold determines whether the bottle is sturdy enough to get out of the moltand able to stand independently. Starting from a dry (!) plaster molt and identical clay-water mixtures you need to figure this out by experiment. (Many factors play a role: composition, temperature, ...)
(The principle for direct casting of forms with appropriate materials is also used for bronze and glass.)
Before the mechanical production of glass bottles stoneware jugs were cheaper than glass.