question: Why do bottles have indents on the bottom
comment: I haven't taken many physics classes, but I believe it relieves the stress on the bottom of the bottle when you squeeze it. This allows the bottle to be able to be squeezed easier and not have the bottom pop out. If the bottom pops out the bottle wouldn't be able to balance on a flat surface.
passages: Thin blown-glass bottles began to appear in Cyprus after the middle of the 1st century BC. The use of the new medium for unguentaria resulted in variations of form, including the thin, "test-tube" type. Glass unguentaria made in Thessaly, for example, often have a distinctive conical body, flared like the bell of a trumpet, or are squat and rounded with a very long neck; they come in a range of colors including aquamarine, pale green, and yellowish green, or may be colorless. This shape was popular in the 2nd and 3rd centuries and is also characteristic of Thrace and Cyprus.
   Section::::Punts.
  
  A punt, also known as a kick-up, is the dimple at the bottom of a wine bottle. There is no consensus explanation for its purpose. The more commonly cited explanations include:
  
  BULLET::::- It is a historical remnant from the era when wine bottles were free blown using a blowpipe and pontil. This technique leaves a punt mark on the base of the bottle; by indenting the point where the pontil is attached, this scar would not scratch the table or make the bottle unstable.
   Even after the pontil rod was replaced by assorted clamping mechanisms known as “snap cases”, many bottles were still being created in the same interesting molds and sold in huge quantities annually. These are known as smooth base bottles and are sometimes found in privies which were in use after the 1860s and as late as the 1880s. Visually, the difference between an early smooth base and a pontiled example of exactly the same bottle is insignificant but to a collector it often means everything. Rare early smooth base bottles can occasionally be as valuable as rare pontiled bottles but statistically they are unlikely to be discovered with any regularity on average privy digs.
   Historically, vla (a popular dairy product with the consistency similar to custard or yoghurt) was sold in long glass bottles. Vla was frequently delivered by milkmen in bottles similar to the long, tapered-neck milk bottles used in many places in the world. However, while the use of the milk bottle streamlined production and distribution practices, the shape of the container made it hard to extract the last bits with spoons, spatulas, or other kitchen utensils. The Dutch answer was the bottle scraper which was perfectly suited to answer this problem.
   BULLET::::- a wire gauze, which itself supports a flat-bottomed beaker or conical flask.
  
  BULLET::::- a large, and therefore heavy, round-bottom flask.
  
  In some cases, a slot is cut in the side of the ring opposite the rod. This is to allow a funnel to be placed upon and removed from the ring from the side rather than from above, a safer procedure.
   While most lever-type bottle openers can be used in either configuration, the designed use can be determined if one of the edges is curved, in which case this edge is designed to sit in the middle of the crown, as the curve concentrates pressure, deforming the crown, and a curved edge does not connect with as much of the crown edge, hence being suboptimal and slipping more frequently if used to connect with the crown edge. This difference can be seen in comparing the traditional opener and contemporary bar blade at right.
  
  Section::::Corkscrews.
  
  Section::::Corkscrews.:Waiter's friend.
   Modern bottles, when moulded, will be given marks on the heel (bottom) of the bottle. These marks serve a variety of purposes, such as identifying the machine used in the production of the bottle (for quality control purposes), showing the manufacturer of the bottle, how much to fill the bottle to, the date the bottle was manufactured, as well as other information. Embossing on a bottle consists of raised lettering, numbers, and/or designs which were intended to inform the purchaser in some way of the contents or to establish ownership of the bottle.
  
  Section::::Characteristics.:Closures.
   Innovations such as the introduction of a working check valve in the nipple (to provide unidirectional flow of the liquid food) appeared as early as 1948 in a patent to J.W. Less, and was picked up by others including Owens-Illinois Glass, eventually making its way into Gerber and all modern pressure-balancing bottle designs, as well as adult drinking cups and various other products requiring fluid flow under vacuum.
   Cortellazzi (1952) of Marmirolo were the first to produce muselets (or wirehoods) in Italy, the brilliant idea of A. Jacquesson who resolved once and for all the problem of bottling sparkling wines: losing valuable effervescence through the cork.
  
  The Cortellazzi brothers (Otello and Evangelista), owners of an artisan shop that had started its business in iron making, the brothers later specialised in the manufacture of wirehoods for Spumante sparkling wine bottles thanks to their invention of the first machine that produces these components out of a single metal wire.
  
  Section::::Modern muselets.
  
  Traditionally, muselets require six half-turns to open.
   BULLET::::- Improved closure strength during shipping
  
  BULLET::::- Regulatory requirement (sometimes)
  
  Section::::Roll-on metal closures.
  
  When an aluminum or plastic bottle cap has an integral band, it is usually connected by thin bridges. They can be molded along with the cap or slit afterwards. When unscrewing the cap, the frangible ring breaks: the ring can separate from the cap, and two separate pieces remain, the sealing piece and the leftover ring; or the broken ring can form a "pigtail" still attached to the cap.
  
  Section::::Shrink bands.
   Some levels have V grooves machined along their bases, enabling the level to sit on a round bar while remaining parallel with the bar's axis. They also have smaller cross levels to enable the second axes to be roughly checked or corrected and to ensure the primary axes' bubbles are at the tops of the vials.
   Caps were originally designed to be pressed over and around the top of a glass bottle to grab a small flange on the bottleneck. 
  
  Section::::Types.:Crown cork.
  
  The crown cork was patented by William Painter on February 2, 1892 (U.S. Patent 468,258). It had 24 teeth and a cork seal with a paper backing to prevent contact between the contents and the metal cap. The current version has 21 teeth. To open these bottles, a bottle opener is generally used.
   Whether mold blown or free blown (both forms of mouth-blowing and considered hand made), most bottles produced before 1860-65 have a distinct scar on their base. This mark is the result of removing the pontil rod. Something which was temporarily fused to the base in order to handle them effectively while they were still exceedingly hot, as their necks and lips were being tooled at the glassworks. The decades just prior to the absence of pontil rods from bottle-glass making were a time when endless variations pertaining to shape, size, style, color and embossing were being produced regularly in an unprecedented quantity. Some of the most interesting bottles were manufactured during this time; 1830s-1860s.
   There are several different types of commonly used closure systems. For glass vials, options include screw vials (closed with a screw cap or dropper/pipette), lip vials (closed with a cork or plastic stopper) and crimp vials (closed with a rubber stopper and a metal cap). Plastic vials, which can be moulded in plastic, can have other closure systems, such as 'hinge caps' which snap shut when pressed. These are sometimes called flip-tops or snap caps.
   Codd-neck bottle
  
  A Codd-neck bottle is a type of bottle used for carbonated drinks. It has a closing design based on a glass marble which is held against a rubber seal, which sits within a recess in the lip.
  
  Section::::History.
  
  In 1872, British soft drink maker Hiram Codd of Camberwell, London, designed and patented a bottle designed specifically for carbonated drinks.
  
  Section::::Design.
   The world's first modern bottle cap, the crown cork, was invented by William Painter in 1890 in Baltimore.
  
  The screw cap using rust resistant aluminum was first used in prescription drug bottling in the 1920s. Molded urea based bottle caps were first introduced in the early 1900s.
  
  A history of accidents involving children opening household packaging and ingesting the contents led the US Congress to pass the Poison Prevention Packaging Act of 1970.
  
  Section::::The manufacture of closures.
   The Codd-neck bottle was designed and manufactured with thick glass to withstand internal pressure, and a chamber to enclose a marble and a rubber washer in the neck. The bottles are filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle is pinched into a special shape to provide a chamber into which the marble is pushed to open the bottle. This prevents the marble from blocking the neck as the drink is poured.
  
  Some older examples had the bullet shape of soda bottles.
  
  Section::::Popularity.
   While tamper-evident bands are not considered a challenge for recycling, it is important that the band stays attached to the cap in case of refillable bottles, because it is hard to remove the rings from intact bottles in an economical way.
  
  The opening ring is a tamper warning: if the seal between the ring and the cap is broken, it is an indication that the cap has been opened.
  
  Section::::Purposes.
  
  Security opening rings might have several possible purposes:
  
  BULLET::::- Provide clear evidence of container being opened
  
  BULLET::::- Deter tampering
  
  BULLET::::- Deter package pilferage
  
  BULLET::::- Deter product adulteration
   Fill line
  
  A fill line is a marking on drinkware indicating the volume of liquid held by the glass. Many countries mandate fill lines on glasses used commercially as a consumer protection measure.
  
  Section::::European Union and Switzerland.
   The most common type of S.C. Dispensary bottle is the "jo-jo" flask, which is a flask with flat panels front and back, rounded shoulders, and a rounding towards the base. These were made and used throughout the life of the dispensary system. Another type of flask, the union flask, was used until the turn of the 20th century, and none were made with the monogram design. Unlike the jo-jos, which all bore the legend "SC Dispensary", unions bore both this and "South Carolina Dispensary". Half-pint, pint, and one quart cylindrical bottles were also made and used.
   Sealed bottles
  
  Sealed bottles have an applied glass seal on the shoulder or side of the bottle. The seal is a molten blob of glass that has been stamped with an embossed symbol, name or initials, and often it included a date. Collectors of bottles sometimes refer to them as Applied seals, Blob seals or Prunt seals.
   After the relaxation of Prohibition in the U.S. in 1936, many breweries began marketing beer in steel cans. The glass industry responded by devising short bottles with little necks, nicknamed stubbies, and types with short necks were called steinies. Capacities varied, with 12oz being the most common size used for soft drinks. The steinie dominated in the U.S. by 1950, and the neck became longer, such as seen with the familiar Budweiser bottle. Stubbies were popular in Canada until the 1980s. Today, standard SP Lager from Papua New Guinea is one of the few beers still sold in 12oz neckless stubbies. The U.S. steinie shape now dominates for small beer bottles the world over, in sizes from half-pint to the European 500ml. The word "stubbie" is now only in common use in Australia.
   It is unknown whether the MG 45/42V had longitudinal gas relief flutes in the chamber designed to help free the bloated cartridge casing from the chamber walls during extraction. Fluting the end of the chamber provides pressure equalization between the front outer surface of the cartridge case and its interior and thus ensures extraction without tearing the tapering part of the case of bottle necked cartridges. Werner Gruner stated that gas relief flutes were present, his colleague Hans-Joachim Kaltmann denied this.
   Section::::Varieties.:Wall-mounted.
  
  Works the same as the lever variation, except that it is attached to the wall, to allow for simpler bottle-opening, which can be done with one hand. The bottle cap can fall into a bottle cap catcher mounted below the opener, or you can retrieve it after removal from the bottle. 
  
  A variant to this are similar types of openers mounted on older vending machines.
  
  Section::::Varieties.:Magnetic catch bottle opener.
  
  This is a bottle opener with a magnet to catch the lids. 
  
  Section::::Varieties.:Multi-opener.
   Later, canteens consisted of a glass bottle in a woven basket cover. The bottle was usually closed with a cork stopper.
  
  Designs of the mid-1900s were made of metal — tin-plated steel, stainless steel or aluminum — with a screw cap, the cap frequently being secured to the bottle neck with a short chain or strap to prevent loss. These were an improvement over glass bottles, but were subject to developing pinhole leaks if dented, dropped or bumped against jagged rocks.
  