Transparent means to allow light pass through the material. This allows the material to look clear and very bright with just one color or a spectrum of colors. If the material does not let light pass through completely it is called translucent. And if the material doesn't allow light to pass through at all it is called opaque.
Depending on how light and the material interact determines the transparency of the object. Light interacts by reflecting,refracting or transmitting with the object. For example water,glass allow light to transmit through them and don't reflect back any light which makes them look transparent. Optical transparency in crystalline materials is dependent on how much light is scattered by the micro structures present inside.
The military is testing on a new material which is transparent and is considered the future material for replacing glass in armored vehicles. This transparent material is called ALONtm. ALONtm is much lighter than glass and can help combat vehicles. ALONtm won't break or shatter like glass and help armored vehicles both on ground and air.
ALONtm is a ceramic compound called aluminum oxynitride. It has high durability and strength in holding up against a .30 caliber multiple armor piercing rounds has made it the material of choice in armored vehicles. ALONtm is scratch resistent which can help the armored vehicles see better in combat situtaions. Airforce is looking at using ALONtm in some of its low flying planes such as the C-130Hercules and helicopters.
The uses of ALONtm are limitless but the cost is still an issue. It is lot more expensive to get large sheets for the widows so researchers are at this point trying to work with the smaller pieces to make them into large windows. But many are optimistic, that this is a material that has many applications and with increase in manufacturing the material it might lessen the costs in the future and more affordable to use.
Another transparent ceramics that has gained interest recently is Alumina. Their applications are being tested specially in lasers, armor vehicles and medical imaging. Alumina is Al2O3 which is also known as Aluminum oxide is an amphoteric oxide and is also known as Corundum. Corundum is in the crystalline form of aluminum oxide. Rubies belong to this group of corundum which due to the impurities present gives the gems their characteristic color. Alumina is found in the ore bauxite which is the principle ore of Aluminum along with other forms of aluminum such as gibbsite and diaspore.
Alumina is used in lighting industry in sodium vapor lamps. It is fired at a temperature of 1800 degrees C to achieve the transparency in hydrogen gas. Alumina is used extensively in ceramics industry because of its low price and high performance
Other transparent materials that are gaining popularity are Yttrium aluminum garnet (YAG).