Rehairing a bow is a common procedure but complex in the steps required of it. Bows for Strings owner and rehairing expert, Nicolas Fyfield, explains his process in this blog post. 

Please note: we provide this article for your interest and information to understand the process of bow rehairing. We strongly recommend you get your playing bow rehaired by an expert.

Step 1: Inspection

First the bow is inspected so one can be aware of any weaknesses or differences from the norm that may need special attention.

Damage to the head and tip face are common and should be repaired before rehairing. Look along the stick and assess its strength as this may affect the amount of hair ultimately used.

Inspect the sides of the ferrule for splits and check the frog, particularly along its base where it meets the stick. This is a delicate area of the frog showing damage when a wedge is forced or an incorrect islet adjustment made. The condition of the pearl eyes, if very worn, can encourage wear to the ebony surrounds and should be replaced.

Focused care needs to be taken with disassembly, especially if the bow is foreign to you. Inspection continues through the whole rehairing process particularly cleaning as removal of accumulated rosin often uncovers the unknown.

Step 2: Selecting the ribbon of hair

After 5.0 gram (approximately 170-180 hairs) is taken from the main hank, unwanted hair is removed (see picture). This hair will vary from hank to hank. The amount rejected will be determined by the initial quality, the cleaning process and how many times the kilogram of hair (or whatever size hank you have bought) is picked over. Good hair is sorted up to 6 times per hair. Poorly treated hair is washed with petrol or bleached; leaching all the natural oils from it making it difficult to work with and should be avoided.

In principle, unwanted hairs are inconsistent with the rest of the hank, can cause different rates of moisture uptake, shrink/expand at different rates and ultimately cause unevenness in the final ribbon of hair that ends up on the bow.  This can mean hair that is:

• Too thin
• Coarse
• Crinkled
• Thick and thin along their length
• Short hair

This sorting process can be tedious - if you let it be - but actually makes rehairing so much easier because the ribbon forms more evenly when setting. After sorting I re-calculate adding more hair if necessary. Using a split gauge measure the even ribbon of hair across its width. 7.5mm for a violin bow is a good guide. Other factors such as the strength of the bow and particularly the players’ request may influence the quantity of hair used. For example, some players may wish more hair to fit down the side of the ferrule.

Step 3: The wedge

Bow hair is set in place by wooden wedges cut in a way that holds the hair firmly in the mortise of the frog or tip of the bow. The mortise is the hole that the wedge fits in.

I use maple left over from bridges cut in our workshop for the tip and frog wedges. For the ferrule or spreading wedge as commonly called I use lime wood. Lime wood is mostly used to line the inside of instruments. It is just the right density to give a little along the grain when inserting.

The way in which these tiny wedges are shaped is critical to the fit and safety in each individual mortise. Wedges too tight for the mortice can cause cracks. When cutting tip and frog wedges, I roughly shape the wedge with a chisel then use a couple of round files and knife to arrive at the final wedge shape.  The aim when cutting the wedge is to lock the hair in place so that it doesn’t come out under the pressure of playing. Taking this into account the wedge should be shaped in such a way as to allow smooth and even passage for the tightly knotted hair below the wedge to emerge from.

Step 4: Tying the knot

Tying the knot is done using a fine fibre in my case nylon filament 0.28mm thick. It can slice your finger when tying. I like its strength and being so fine it creates a slim knot. After tying apply glue to finish, making sure it infiltrates the very end of the knot. Principally a well tied knot should prevent any slipping of hair and bunch it, reducing the end of the ribbon to a manageable size that allows a comfortable fit into the mortise.

Step 5: Comb

After the first knot is tied and wedged the hair is moistened to make combing easy. Two combs are used in the process of forming the ribbon, the finer of the two an ordinary lice comb. The hair will take in moisture depending on its porosity, hydration and oiliness and this uptake will influence the elasticity which will in turn contribute to judging the final length tied. The aim is to make the hair easy to manipulate into an even ribbon, not absorb a great deal of moisture which will cause the comb to snag. Imagine the hair after combing, wedged at one end of the stick, the rehairer holding 170 hairs at the other end, then tying the knot. It conjures a delicate moment in the process given you have about one millimetre to spare.

Step 6: Drying

Most rehairers will insert wedges first at the tip, second at the frog and last at the ferrule which allows the hair to be spread into the neat ribbon we are familiar with. Finally the hair must dry before applying rosin and at this point it may shrink depending on the ambient temperature, humidity and the hair itself. Whether it shrinks evenly will depend partly on how well you have sorted the ribbon of hair to begin with. 

May your hair run straight.