Guido, >after some efforts i have calculated my vertical declining sundial, and it >seems to work fine. >Now I have the problem to draw the final hour lines on the preliminary ones >(drawn with a pencil), but the wall surface has many granules and it is >difficult to obtain sharp edges for these lines. >Could you please help me? Which is the best kind of varnish to be used? >Which is the best technique for lines drawing?
Tony Moss has made a number of excellent suggestions in his previously posted note. I would like to add, that if you chose to paint lines directly on the wall, you can first use a sharp tool with a straight-edged guide, and scratch their locations into the surface, deeply enough to show through paint that may be used to renew the background coating at some later time. (This is independent of Tony's suggestion of cutting "Vee" grooves.) Depending on any suface paint already present, you can use exterior grade enamels or exterior grade latex trim paint. Latex seems to adhere quite well to masonry. There is an old fashioned type of drafting pen which has a pair of opposed steel points, shaped like the backs of tiny spoons (but flat, not concave on the inner sides,) and provided with an adjusting screw to set their tip's separation against their tendency to spring apart. Their separation controls the width of the line drawn, over a wide range of thicknesses. Although traditionally used with India ink, I have often used one with enamels and with latex paints. To place the paint between the blades, I use an inexpensive watercolour brush. (The paint must not get on the outside of the pen's tips. Use fairly thick paint, and experiment until the line's width is as desired. You will need a straight (wooden) edge-guide that has a bevel, or is undercut, so that the paint for the line will not accidentally touch where the wood meets the masonry and be drawn between by capillary wetting action. If you can't make a penline as wide as you want, you can often draw two lines of the greatest thickness you can draw, to define the outer edges, then fill in between later, using the pen or a brush, still with a straight guiding edge. When drawing on the vertical wall, it is best to keep the guide on the upper side of the line, in case of an accidental "run." Keep some paint solvent and a rag handy! I prefer to use latex because it is so easy to make corrections with soapy water, if you do so before the paint hardens. (Be sure to rinse away the soap with clear water, or it may weaken the paint's adhesion and/or durability.) Bill Maddux
