Bоttle cоllecting is а relаtively inexpensive wаy tо preserve some of the most beautiful and breakable items of the past, as well as a way to invest in the future. A bottle collection will appreciate over time if the beginning collector knows how to assess each bottler's potential value and buys wisely. Although rare sizes or the appearance of bubbles formed during the "fining out" process can increase a bottle's worth, perhaps the quickest way to assess value is by determining a bottle's age: old bottles, generally speaking, are more valuable than newer ones and can be identified according to what they originally contained - - medicine, bitters, mineral water, or fruit, for example. Color also helps identify a bottle's age and hence its potential value. Bottles made of glass - mixture of sand, soda and lime heated to a molten 1,000-2000 degrees Fahrenheit - - assume a color dependent on the mineral content of the sand, the proportion of sand to lime, the temperature of the furnace, and the length of firing. Until the late 1800s, most bottles were green, due to the iron content of the sand. When food manufacturers began to demand clear bottles, however, manganese was used to remove green and other naturally occurring colors such as brown, amber, and aqua from glass. Therefore, most clear bottles date from the 1880s on. Of course, a variety of other colors - -such as yellow, cobalt blue, purple, and red - - were also created by adding metallic oxides to the raw materials. Another quick way to date bottles is by looking at the mold seam - -a thin line running up the bottle's length-in conjunction with the bottle's lip, which is the trim around the finished top. Seams occur where two (or three) separate blown sections are joined. On bottles made before 1860, seams barely extend to the bottle's shoulder (the area where the thicker body slopes upward into the narrower neck). In bottles made between 1860-1880, the seam runs completely up the neck to meet the lip of the bottle. After 1900, when bottles started to be completely machine-made, the seam runs through the lip. Prior to 1840, lips were created by simply snipping the neck free in a blunted end resembling a tube, hence the term "sheared lip." From 1840 to approximately 1880, glass rings of various shapes and sizes were attached to the end of the sheared lip, resulting in what is known as the "applied lip." After 1880, the shape of the applied lip was more or less standardized to appear as it does today on popular soda bottles. A bottle's weight can also indicate age - - heavier bottles are often older - - as can other factors, such as the appearance of a certain kind pointil mark. But for the novice collector, just a few beginning guidelines can help identify older and potentially more valuable bottles that will, perhaps, appreciate over time like some cathedral pickle jars did -- by 400% in 20 years! Passage 1 Question 2: The implied main idea of paragraph four is