1. It has previously been reported that applying a glass,
Background and Objectives
It has previously been reported that applying a glass,
microscope slide to the skin during Q-switched Nd:YAG
laser treatment of tattoos can result in less pain sensation.
Small ‘pits’ were observed in the glass after treatments.
These pits are created by high-speed ink particles leaving
the skin during treatment.
This short, preliminary study investigated whether there
was a possibility of bacterial contamination within
these pits.
Study Design and Methods
Optical microscopic analysis (GS S.E.R.B. P2 microscope)
revealed the presence of particulate matter in the pits.
Gram Stain analysis reveals the potential of bacteria,
although the source of this bacteria has not yet
been established.
Further analysis, such as PCR, is required to determine
the viability and source of the bacteria.
Results and Conclusion
The red colouring within fragmented glass slides post-laser treatment appears to reveal the presence of Gram negative bacteria.
Kinetic energy calculations reveal that these particles may be leaving the skin in the range 1 to 100 m/s (or possibly higher!) Standard gloves and masks offer poor protection against these high-speed, microscopic ink particles.
This indicates the possibility of cross-contamination from ink particles leaving the skin during and photo-mechanical laser treatment of tattoos.

2. The glass slide used on this tattoo clearly shows a ‘swirly’ pattern similar to the tattoo text, following treatment with a QS Nd:YAG laser (4.5 J/cm2, 5 mm spot diameter, 1064 nm, Type 2 skin, 26 y.o. female, first treatment). Against a white background the particular imprint appears almost reddish/brown even though the original tattoo appears to be blue/black.
The photomicrograph on the right (magnification 160X) reveals particles in the range 0.05 – 0.5 mm on the glass. However, these particles are clearly sitting on the glass surface as they were easily removed using an alcohol swab. In many other instances the particles remained after cleaning, indicating that the particles had been embedded within the glass.

3. Red patches within embedded tattoo fragments
Photomicrographs of Gram Stain results
Red patches within embedded tattoo fragments
The black areas are sub-millimetre, fragmented ink particles embedded in glass slides following QS Nd:YAG laser treatments. The graduation marks are 0.12mm apart.
These images indicate the presence of red patches surrounding the ink particles, possibly due to Gram negative bacteria.

4. ‘Insect-like’ appearance of ink particles
Some of the embedded ink particles appeared in an almost ‘insect-like’ formation. The author suspects that these are generated by the melting of the ink particles as they rapidly lose kinetic energy within the glass. Most of this energy is converted into heat energy which raises the temperature of the ink particles to above their melting point.
At this point they become more fluid and hence ‘spread’ out resulting in these ‘insect’ formations.
Initial calculations based on the approximate size of the particles, the Young’s modulus of glass and the estimated depth of penetration of the ink particles suggests potential ‘escape’ velocities of tens, perhaps even hundreds, of metres per second!