Chlorine test

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In Brief

The laser can successfully cut many materials that are damaging to the laser when cut. Do not think that just because the laser can cut it, it is acceptable to do so.

In particular chlorinated materials create fumes which destroy laser components, primarily the optics. These are very expensive to replace. All unknown or unproven materials must have a sample tested for chlorine prior to cutting them in the laser.

Burn copper wire with a torch until green flame stops. Continue heating copper wire red hot. Jab still-hot copper wire into sample piece away from flame (below flame works best). If green smoke or flame ensues, there is chlorine in the piece and it cannot be used inside the laser cutter.

Known Materials

Acceptable:

• Acrylic plastic, clear or colored
• Wood & wood veneers
• MDF
• Cardboard
• Leather
• Fibreglass cloth (no resin)
• Glass (etching only)

Unacceptable:

• PVC plastic. PVC = "PolyVinyl Chloride". The "chloride" means it has chlorine.
• Sintra
• (Incomplete List)

Introduction

The Beilstein Test: Screening Organic and Polymeric Materials for the Presence of Chlorine, with Examples of Products Tested

http://www.cci-icc.gc.ca/publications/notes/17-1-eng.aspx

http://www.cci-icc.gc.ca/publications/notes/17-1_e.pdf

Chlorinated organic materials are generally considered unsuitable for long-term conservation and museum applications due to their potential harm to objects. These materials may degrade and produce acidic gases, or additives such as plasticizers may migrate to objects. These products can be analyzed in detail in the laboratory, but conservators may use a simple test — the Beilstein Test — to screen their own materials for the presence of chlorine without having to submit samples for laboratory analysis.

The test is based on the reaction of chlorine with copper compounds at the high temperatures found in burner flames. These conditions produce excited, green-coloured copper atoms or ions that cause the normally colourless (or very slightly blue) flame to flare brilliant green (or sometimes blue-green).

Procedure

You will need:

• Thick copper wire (A tube of these is in the Trotec PC drawer)
• Pliers
• Propane torch (Usually found in the welding area)
• A small sample of your material

Use a pair of pliers to hold the end of the wire in the flame for a few seconds

Stab the still-hot wire into a sample of your test material - try to get a decent amount of it melted on there

Put the wire back in the flame

If the flame emerald green, chlorine is present in the material and it must not be used in the laser cutter.

If the flame remains blue or orange your sample does not have

Discussion

The Beilstein Test has been used for many decades to analyze organic and polymeric materials (Shriner et a1. 1964; Vogel 1966). A very similar test is now used by refrigeration technicians to detect and localize leaks of freon-type refrigerants (i.e., chlorinated and fluorinated hydrocarbons). This test has also been recommended for detecting PVC coin storage products (Sharpless 1980).

The Beilstein Test is quite sensitive and requires a very small sample. There are, however, several possible sources of error. Residues from fingerprints can give weak false positive results. Chlorinated inorganic materials (i.e., pigments, fillers) can also give a false positive result, but these are usually not present so they rarely interfere with the test. The major difficulty encountered is that the sample may volatilize too rapidly, especially if it is a solvent. These volatiles are lost so quickly that they do not have time to react with the copper wire. To avoid this problem, the fourth method described above — introducing the fumes at the air intake for the flame — is recommended.

The test is suitable for screening a wide variety of products including plastic films and sheets, adhesives, rubbers, coatings, solvents, and fabricated items. Common materials that give positive results include poly(vinyl chloride), poly(vinylidene chloride), chlorinated rubbers, chlorinated epoxies, chlorinated solvents, and any compositions containing these materials.

The Beilstein Test has been used to examine a variety of materials at the Analytical Research Services laboratory at CCI. The presence or absence of chlorinated organics was confirmed by infrared spectroscopy or by radio-isotope excited X-ray energy spectrometry. The results are presented in the tables below.