This is a follow-on from my previous thread about the toothing on Iwasaki carving floats. I remarked there that the surface left by the floats seemed "shinier" than that left by a good quality fine-toothed rasp (Liogier cut-14 modeler's rasp). The purpose of this thread is to try to understand what's going on at the wood surface to create that impression.
I grabbed a random piece of offcut, which happened to be the edge of a piece of plainsawn birch, hence a quartersawn surface. I first worked the surface with the Liogier rasp, sawed off a ~3/16" thick section (kerf included), and then worked the resulting surface with an "extreme fine" Iwasaki carving float before sectioning again. I wiped each surface to remove loose debris, but did not otherwise work them. In each case I worked the tool close to the grain direction but not exactly along the grain.
Here are 3.6 x 2.4 mm sections of each, imaged at ~1.3 microns/pixel. I used one grazing light source from above (perpendicular to grain/tool directions) to accentuate surface profile differences. These would both look a lot smoother under "head-on" lighting. The camera is looking straight down on the wood, such that it doesn't really see specular reflections or shininess in general. The left image is the rasp, and the right image is the float:
birch_liogier_14.jpgbirch_iwasaki_xfine.jpg
I think that the pictures speak for themselves. The results with the Iwasaki are smoother, with most discontinuities arising from the wood's pores rather than the tool itself. It's not as good as a plane can achieve, but it's very good for a freehand shaping tool. I worked the Iwasaki in basically the same direction as the rasp (slightly up and to the left), and I don't see much going on along that axis. The Liogier rasps's teeth do cut very cleanly as evidenced by the minimal tearing to the wood fibers, but the fact that they form a non-planar surface can't be hidden.
For a sense of scale, the large pore just left and above center of the Iwasaki image is about 6 mils (0.006") wide. The tracks from the rasp are maybe double that.
I think the rasp very much has its place and strengths (the Iwasaki is a lot harder to manage for complex forms IMO) but so does the float.
Geekish details: Canon 1Dx II and MP-E 65, 5X magnification, cropped down to half size. Canon MT-24EX flash, one head active, grazing from above. RRS TP-243 tripod, Arca-Swiss d4 head, RRS B150 dual-axis focusing rails.