Between the reflection and transmission types of holograms, many variations of holograms can be made. One such popular variation is the embossed hologram. Embossed holograms are the type of holograms used widely in most security applications. They offer an effective method of protection against any forms of manipulation, as they are too difficult to copy due to their complex technical structure. Almost all credit cards and passports have embossed hologram. One of the most common example of an embossed hologram is the "eagle" in any Visa card. These holograms are easily produced in mass quantity at a very low cost. Embossed holograms have become very popular for various purposes, like advertisement, promotion, security labels, plastic cards etc.

Properties of Embossed Hologram

Some important properties of embossed hologram are as follows:

• Embossed holograms have shallow hologram depth. The depth is usually a few millimeters.
  
  
• The cost per unit when mass-produced is very low.
  
  
• Embossed holograms are durable and flexible.
  
  
• One of the peculiar feature of embossed hologram is that mass production can use existing equipment and technology, like in CD production.

Process of Making Embossed Hologram

Embossed hologram is a kind of white-light transmission hologram which is applied to a reflecting relief surface. This helps in diffracting light. In the first place, a transmission stereogram is printed on a light-sensitive medium. This medium is engraved to form a microscopic relief pattern that is similar to the interference pattern of the holographic image.

Ideal Embossed Hologram The "Ideal Security Embossed Hologram" should satisfy the following factors: Should include variable information. Should include buried multiply connected hologram. Should include information. Should be machine readable. Should not be "human readable" without a reading device.

When developed, the hologram is made up of grooves on the surface. A layer of nickel is coated on this hologram and then peeled off, which results in a metallic "shim." In the same manner, various secondary shims are produced from the first one. The shim is placed on a roller. On account of high temperature and pressure, the shim presses or embosses the hologram onto a roll of composite material. Embossed holography is a technique or a process which mechanically copies holograms for mass production. These embossed holograms diffract incoming white light into rainbow colours and simultaneously reconstruct the holographic image. They are also called rainbow-holograms at times.

What are needed to produce embossed holograms?

These holograms can be produced from any of the following:

• Graphics artwork like for example, company logos, texts, images for 2D/3D-holograms.
  
  
• Three-dimensional objects in scale of 1:1 for 3D-holograms.
  
  
• Specially produced film-sequences and computer-animations for holographic stereograms.

Diagrammatic Representation of the Making of Embossed Hologram

The following figures (Fig 1-Fig 5) illustrate the process used in making embossed holograms:

Advantages of Embossed Hologram

Some advantages of embossed holograms are as follows:

• Embossed holograms have a decisive cost advantage for large-volume applications like in credit cards and telephone cards.
  
  
• They can be applied by hot stamping.
  
  
• These holograms are thin enough to be used on thin, flexible items like paper currency and travelers' checks.
  
  
• The greatest advantage of embossed holograms in some applications is the fact that they are more durable than other holograms.
  
  
• The embossed holograms provide the benefit of multiple colors.

Disadvantages of Embossed Hologram

Some disadvantages of embossed holograms are as follows:

• The production of an embossing master is very time-consuming.
• The production of embossed hologram is a relatively expensive process.
• The major disadvantage of embossed hologram is that it lack depth.

Applications of Embossed Hologram

Embossed holograms are used in a wide variety of applications such as follows:

• Packaging films
• Paper
• Decorative laminate
• Foils
• Labels
• Automatic labeling
• Screen printing
• Window patching
• Security applications specially on visa cards