Density gradient laser targets with decreasing density or increasing stepwise density layers were reported in experimental and theoretical papers on astrophysics modeling, equation-of-state (EOS), and shock-wave dynamics studies. The research with targets of smooth density gradient is due. The experiments with gel-catalyst concentration diffusion are discussed for density gradient foam formation. We used multi-image X-ray tomography for measurement of the silica gel layer density gradient in the process of its growth. Gel with a density gradient growing from a flat boundary between a gel-forming solution and a catalyst solution has been investigated through a set of three-dimensional frames of an X-ray computer microtomograph. Laser targets require high (>1 gcm-3/cm) density gradients of the spatial profile for EOS experiments. The first targets from silica aerogel with a density gradient are demonstrated. Yet these targets perform less density gradient (<0.1 gcm-3/cm) than is required for pressure multiplication in EOS targets.