Terry Richardson, Senior Instructor of Astronomy & Physics at the College of Charleston designed a "Make Your Own Safe Solar Viewer" for the upcoming solar eclipse, sunspot cycle 25 and beyond. This set includes our L14810 achromat (52mm diameter by 600mm focal length) and a Barlow lens with a focal length of -27mm. For the achromat: Place the crown (double convex) with its strongest curve against the negative side of the flint. Use a couple pieces of masking tape on the edges to hold them together. The crown side faces the sky. Using an achromat instead of a single element lens you will get to see more of the sunspots and less blue fringe around the sun (chromatic aberration).
Here are the college's links for instructions and additional information: https://richardsont.people.cofc.edu/safe_solar_folder/the_2-lens_SSV.html