Impressioning

=Impressioning=

Impressioning is a non-destructive, covert method of creating a working key for a lock without picking or disassembly. Impressioning is one of the most useful skills in locksmithing, and is divided between copying and manipulation techniques. Copying focuses on making negative-image molds of a source key, while manipulation uses various techniques to determine the proper heights of internal components. Impressioning via manipulation is closely related to decoding.

Impressioning has been long used to obtain a working key for a lock by locksmiths, locksport enthusiasts, and criminals. Many high profile crimes have been accomplished through the use of impressioning techniques. Techniques of impressioning have been applied to forensic investigations to aid in serial number recovery and tool mark identification.

History
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Key-based (copying) Impressioning
Key-based (copying) impressioning focuses on obtaining a source key for a target lock to produce a copy of it. The process involves two stages, first creating a negative-image of the source key in a soft material, then casting a positive-image (duplicate) key via the negative-image. The casted key can be used to open the lock or further duplicated into a stronger material. Time required for key-based impressioning depends on the material used to create both negative-image and casting.

Tools Used

 * Casting Material
 * The material used to cast a working key once the negative-image is produced. Usually a low melting point metal, epoxy, or silicon.


 * Impressioning Material
 * The material that the negative-image is produced on or in. Usually wax, clay, or silicon.


 * Knife
 * Used to remove excess material displaced by the source key. Also used to provide a heat escape in the impressioning agent once the negative-image is produced.


 * Lubricant
 * Used to prevent the source key from sticking to the material and deforming the negative-image when the key is removed.


 * Mold
 * A container used to hold the impressioning agent, generally a square or rectangular box with one side removed. Often referred to as a "clam shell" or "clam kit."


 * Paintbrush
 * Used to apply lubricant to the material.

Internal Component Impressioning
All non-copying impressioning techniques rely on the ability to bind internal components until they are in the correct position. In modern use, components are bound and impressioned against a blank key to produce marks that indicate their positions are incorrect. Once marks stop appearing the component is no longer binding and is properly aligned within the lock. The process for this method of impressioning varies slightly depending on the lock design and included high-security mechanisms.

In warded locks, an impression is taken of the wards directly.

The general impressioning process is as follows:
 * A proper key blank for the lock is obtained.
 * The key blank is prepared to enhance markings.
 * The key is inserted into the lock and manipulated to produce markings on the blank.
 * Markings are interpretted and material removed from the key where binding is suspected.
 * The process repeats until all components are at the proper positions and the lock opens.

Blank Key Selection
The blank key selected for impressioning must match the lock specifications exactly. This includes the keyway, component count and spacing, and any additional security features. Failure to select the proper blank may prevent it from being inserted, able to receive markings, or able to open the lock due to additional security features.

Blank Preparation
For pin tumbler locks, the blank is usually prepared by using a fine file to clean the top edge of the blank to leave it with a uniform texture. This is also sometimes the case with wafer locks as well, but another method which many employ with great success on wafer locks is to file the side of the blank to leave it with a blade-like edge. Personal preference plays a great deal into blank preparation.

Sometimes other parts of the key blank are modified as well in preparation for impressioning. For example, M1 blanks for standard Master Locks sometimes have a shoulder which is too tall for impressioning due to the 'slop' in the lock. Without removing some of the top of the shoulder, it will 'bottom out' on the face of the lock before it actually allows the pins to bind.

Obtaining Marks
After the blank is selected and prepped, it is typically inserted into some kind of vice. Many companies offer locksmiths vices specifically for impressioning, but others rely simply on a pair of four inch vice grips. The key is then inserted into the lock. There are several different ways to obtain marks:


 * Pull-out method
 * The blank is inserted, and then turning pressure is applied. By withdrawing the key while applying pressure, sometimes small lines can be seen. Some specialty tools are made specifically for this, which have a trigger to pull the key out slightly.


 * Rocking method
 * The blank is inserted, and then turning pressure is applied. The key is the rocked up, against the pins, to obtain marks. Sometimes the key is tipped before applying turning pressure to isolate marks. For example, if the key is tipped with the tip upward, and then rocked so the head goes up, the marks closer to the head will be easier to identify. The opposite is also true, where the tip starts down and is rocked up. In that case, the tip will show more marks if there are any.


 * Bumping method
 * The blank is inserted, and turning pressure is applied. A strike is then applied to the head of the key from a small mallet for example. This strike against the binding pins leaves marks.

Interpreting Marks
After obtaining marks, the key is taken out of the lock for inspection. Sometimes aids are used, such as magnifying glasses or even different color lights. In pin tumbler locks, pins leave small circular marks. They will be a uniform distance from the edge of the blade (although not always centered), and from each other. In contrast, wafer locks tend to leave more rectangular marks, and they are very often found on the edge of the blade. It is for this reason that sometimes blanks are "knife edged" in preparation for impressioning, because wafer locks will 'crush' the knife edge away and leave very obvious marks.

Filing Marks
When a mark is identified, the next step is to file that cut. Some chose to use a code machine to cut the key down to the next possible known depth in that space, but others (or those lacking the equipment, will use a fine file. Very little is taken off at one time, depending on the particular lock. For example, Schlage locks (and many other locks) use ten different depths, so not much will be taken off. In contrast, some wafer locks (such as many of those in cars) have only four or five depths, in which case a little more may be taken away. Special care is given to the width and slope of cuts, as to not interfere with nearby marks and also allow for easy insertion and withdrawal of the key. If the slopes on a cut are too steep, the key may not enter or may get stuck in the lock.

Final Steps
When a pin reaches the correct height, it will no longer bind against the plug when turned, and will therefore no longer leave marks in that spot. Once all the pins are at the correct height, the plug will turn.

At this point, the key can be cleaned up by more carefully sloping edges, and taking off any sharp points. Sometimes a micrometer will be taken to the key and cuts will be rounded to the nearest known factory cut to produce a key by code.

Keys which have been used in impressioning are typically not used long, because they become exceptionally weak from being bound in the cylinder repeatedly.