## 4 Conclusions  
This article presents high-speed images of metal transfer in pulsed GMAW acquired at different settings. Two narrow bandpass filters were used with varying camera exposure times to yield quality images revealing the features of the arc, droplet, and weld pool, without a need for external light sources. These are useful results, given that it provides guidelines for producing images that contain useful information regarding arc behavior, metal transfer, and weld pool phenomena for those who study these features either numerically or experimentally.  
Using the images acquired, arc length was measured, as defined by the British Standard Institute [2] and American Welding Society [3], and the relationship between arc length and arc voltage was evaluated. It was found that for low values of current, when the electrode vaporization rates are low, the proportionality between arc voltage and arc length holds true; however, for higher current values, where increased vaporization of the wire electrode tip occurs, the measured welding voltage increases, even though the arc length decreases. For high values of welding current, the results suggest a relationship between the measured welding voltage and the diameter of the arc core, which is composed of a high fraction of iron vapor. There appears to be a linear relationship for different current values, but further study is required to generalize this relationship. This discussion on the arc length aims to corroborate the discussion of [PERSON] [1], which points to the need for a more rigorous definition of arc length which includes the variety of weld processes available.  
Figure 8: (**a**) schematic geometric features measured; variation of welding voltage with metal vapor column (**b**) height, (**c**) diameter at the cathode, and (**d**) ratio between diameter and height. The high-speed images were taken using the 515 \(\pm\) 10 nm wavelength filter, exposure time of 6.25 \(\upmu\)s, and lens aperture of f/22.  
**Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/7/5/503/s1](http://www.mdpi.com/2076-3417/7/5/503/s1)]([http://www.mdpi.com/2076-3417/7/5/503/s1](http://www.mdpi.com/2076-3417/7/5/503/s1)), Video S1: This video shows the drag of metal vapor from the secondary droplet to lower temperatures arc regions leading to future formation, Video S2: Comparison of arc plasma and metal transfer for different camera settings and filter selections.  
**Acknowledgments:** The authors acknowledge Natural Science and Engineering Research Council of Canada (NSERC) and TransCanada Pipeline Ltd. for the financial support and Liburdi Engineering Limited for the technical support.  
**Author Contributions:** [PERSON] conceived, designed and performed the experiments; [PERSON] and [PERSON] assisted with measurements and data collection; [PERSON] and [PERSON] contributed to the discussion of the experimental data; [PERSON] and [PERSON] wrote the paper.  
**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.