Spatter refers to the small droplets of molten metal that are thrown out of the arc and weld pool and solidify on the surrounding surface. It wastes filler metal, spoils the appearance of the joint, and requires extra cleaning, so controlling it is an important part of good welding practice. Spatter is fundamentally a symptom of an unstable arc — when the arc length (the gap between the electrode tip and the work) becomes too long, the arc voltage rises and fluctuates, the metal transfer across the arc becomes erratic, and large globules are violently expelled instead of transferring smoothly into the pool.

Why reducing arc length slightly is correct: A shorter, more controlled arc lowers and stabilises the arc voltage, promotes smooth droplet transfer, concentrates the heat, and therefore directly cuts down spatter without changing the electrode, current, or the metallurgy of the weld — so weld quality is preserved. This is the most targeted fix for the actual cause.

Why the other adjustments do not work:

• Switching to a larger electrode would demand higher current and deliver more molten metal to the arc, generally increasing the amount of spatter rather than reducing it.
• Decreasing base metal thickness is a property of the workpiece, not of the arc; it has no bearing on arc stability and is usually not even an available option for a given job.
• Increasing travel speed marginally mainly reduces heat input per unit length and can cause a narrow, poorly fused bead; it does not correct the arc instability that produces spatter, and pushed too far it harms weld quality.

Hence the best corrective action is to reduce the arc length slightly.