What is a bow pen?

John asks: Reading with great interest your article on painting the Speedline Pilot Boat. Sounds very much like me to a tee! The part that intrigued me was your reference to using a "bow pen" to outline the silver wheelhouse window-frames. I have not heard of this before, could you enlighten me?

I am restoring an elderly Caldercraft model of the Clyde Pilot Boat, and feel the pen would be a boon for high-lighting the port-holes in brass.

Bow pens aren't the common instrument they were in those black & white days. Then, every draughtsman would wield one with aplomb and all schoolchildren found one in their geometry sets. Now it's all Computer Aided Design and kids don't know they're born and wagons wheels have got smaller etc.

A bow, or ruling, pen is an instrument for drawing lines with ink or in the case of modelmaking, paint.

The pair of steel jaws are set a tiny distance apart using the knurled nut on top. The wider they are apart, the wider the line you draw. Skilled users can produce neat lines a fraction of a millimetre wide.

To use the tool, place a drop of paint between the jaws using the end of a tiny screwdriver. You don't want paint anywhere but in between then so wipe off excess with the paper towel. Next, try drawing a line on some paper or (in my case) the edge of your modelling board. If it's right, proceed to the model if you are feeling confident. If not, adjust the width and try again.

Neat enamel works well as does Humbrol acrylic. You don't want to thin the paint if possible as it tends to come out on a blobby rush.

Cleaning the pen depends on the design. The one shown, which I inherited from a proper old-school draughtsman allows me to swing the bottom jaw out of the way without adjusting the gap. My old school set doesn't have this so you dunk it in thinners and then fiddle around wiping the ink/paint out.

Whilst very useful, this is a tool that demands practise to get the best from it. I'm not very good but was able to run a line around the edges of the windows of the boat mentioned so I could them paint up to them with a brush. It's quite useful for locomotive "wasp stripes" too. With practise and luck, a straight line is reasonably easy to draw for neat edges.

A quick search will normally throw up bow pen suppliers - Golden Arrow do some useful looking sets. You are often advised to buy the best you can afford but for the beginner, a stationery set version will allow you to play and decide if it's worth upgrading. Try eBay too as there's always some in the Finescale Model railways section and this is a tool it can be worth buying second hand as you might get a top-notch model on the cheap.