Is my chlorine sample real?
At $\pu{20 °C}$ dynamic viscosity of liquid chlorine is about $\pu{0.35 mPa·s}$ (see Figure 4 from [1, p. 7]), whereas dynamic viscosity of water is about $\pu{1 mPa·s}$, e.g. water is nearly 3 times more viscous at room temperature than liquid chlorine, which should not appear that thick.


Figure 4. Viscosities of chlorine gas and liquid.

Note that your perception of viscosity and &quot;thickness&quot; may be distorted due to capillary effect if your chlorine sample is sealed in a tiny ampule.
References

Chlorine: Principles and Industrial Practice, 1st ed.; Schmittinger, P., Ed.; Wiley-VCH: Weinheim; New York, 2000. ISBN 978-3-527-29851-8.