The moment Lin Mu touched the surface of the Liquid Gold, he felt the difference.
It was dense enough that his body was repulsed by it a bit. If it were not for the fact that he had already absorbed a relatively high amount of gold in his body, he might not have even been able to sink into the liquid gold.
After all, the density of gold was way higher than that of the human body, making it close to impossible to sink into it.
Even then, the density of the liquid gold in the cauldron was way higher than the gold Lin Mu had refined before this. Thus he had to force his way into it. If he didn't put a constant pressure, he would be pushed out of the gold.
Thankfully, his body was no longer affected by the heat of the gold and could withstand it with ease. The previous two steps had increased his defense to handle that much with ease.