When casting into my CNC moulds as a tester. I wanted a grogged outside surface with a smooth interior. To achieve this I first added the grogged mix at 15% for 5 mins, tipping out and then added smooth slip for a further 5 mins. As you can see by the image below, there was still uneven marks and grog visible. I then tried the same percentage with 3 mins grogged mixture, and a 7 min smooth slip cast. This improved the finish but was still visible. I will continue to explore this further as when removed from the mould, the grog on either timing was not visible.
I then sprinkled grog on the surface of a puddle of slip, it didn’t sink in and was left along the surface so maybe I can able it after like a textured glaze.
I then increased the percentage of the grog to slip ratio to 75%, a huge jump in an attempt to see the grog on the outside surface. I found the higher the percentage, there was a positive increase in spots on the inside surface with no change on the outside. Along with this, the higher grog concentration left the slip unable to shrink inside the mould, making it unable to remove without washing out with water.
I found these experiments helping in my understanding of slips and although I did not achieve the results I was hoping for, the image below shows a piece of 75% grogged slip with the texture on the inside surface. This is close to the texture I hope to achieve on the outside when casting my final pieces after more testing.