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 duplicate key using 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.

Manipulation-based 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 the component is properly aligned it should no longer bind or produce marks. The process 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 process is:

• A proper key blank is obtained.
• The blank is prepared to enhance markings.
• The key is inserted, components are bound, and key 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 in 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.

The material of the key blank selected is important; stronger metals, such as nickel-silver or steel, should be dismissed in favor of softer brass, aluminum, or lead based keys. The softer material makes it easier to produce and analyze markings, but the material must be strong enough to withstand torque applied during the impressioning process. Various proprietary key designs exist to enhance markings while maintaining strength.

Blank Preparation

Preparing the blank key is meant to enhance the marks left by components. To begin, the blank may be lightly filed to produce a smooth surface. Care is taken to ensure that filing does not exceed the first depth of the key at any point before the impressioning process begins. The bitting surface may be filed to a knife edge to thin the bitting material, thus making it easier to produce impressions.

In the case of lever locks, the blank may be coated with something to make identifying marks easier. Traditionally carbon was used and the bitting of the blank key was "smoked." This is still popular in modern use, but other materials, such as paint, are acceptable.

The key blank may also be modified to allow for enhanced movement within the lock, such as thinning of the blade or removal of material from the shoulder or tip.

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. Specialty tools are available 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. Visual aids may be used, such as a magnifying glass, different color lights, or a microscope. 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.

Tools Used

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Pressure-responsive Impressioning

In the case of dimple locks, a specially prepared key may be used in conjunction with pressure responsive materials to automate the process of manipulation-based impressioning.

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