Ó 2000-2001 Stephen A. Shepherd
This technique has been around for centuries. Shellac is a thermoplastic medium; it becomes semi-liquid when heated and hardens back to a solid mass when it cools. By using a heated knife the hard shellac can be melted and forced into cracks, voids, lacuna or just missing finish and be smoothed to the surrounding surface. One of the least invasive method of repair, it is also quick and easy, once you get acquainted with the nature of the tools, materials and techniques. An advantage of hot stick repair is that the surrounding finished surface can be preserved and the knife can produce an optical flatness to match even the most high gloss finish. Allowing for a very selective patch, spot repairs can be accomplished without a major restoration project. The color match needs to be done in the same lighting as where the piece is located. Use natural daylight or color corrected lighting to insure you don’t get color shifts with changes in lighting.
The traditional method of heating the knife was to use a soot-less flame such as an alcohol lamp. The knife is of smooth thick metal that can take and hole heat and at the same time capable of forcing the melted shellac into the voids. A knife can be made from putty knives, painting knives, pallet knives, spatulas or any metal that can be shaped and formed into a useable shape. An old kitchen knife or even a stiff piece of flat metal can be fashioned into a burn-in knife. The requirements are some flexibility and enough mass to hold enough heat to allow the tool to transfer the molten shellac or lacquer stick to the area being repaired. A wooden handle to isolate the heat in the blade and prevent burning is also a good idea. The knife needs to be shaped to allow for applying and smoothing the hot shellac to the surrounding surfaces. The surface must be smooth and free of blemishes to produce a smack smooth finish. Texture can be added but this is done after the surface is smooth. Any nick or dent on the knife will be transferred to the shellac repair, so keep the knife well maintained. I prefer a flat blade that is bent to a curve on the end. This shape gives an inside curve for holding and transferring the molten shellac to the lacuna and the outside curve is helpful when flattening and smoothing the stopping. The flat blunt front edge can be used to add textured grain into the infill.
First the knife is heated, and then cleaned off on a cloth rag. It is then re-heated and touched to the shellac stick and a small amount is brought onto the knife. If it is hot enough it is then placed over the void or crack and the molten shellac is pressed into the area. The knife may need to be re-heated to make the shellac molten. Be careful, as the shellac will catch on fire. I wave the knife in the flame and clean off any residue on the cloth rag and re-heat the knife. Then collect some more shellac and work it into the void. Once the lacuna has been replaced and the void is adequately and sufficiently filled, it is time for the smoothing.
This is the most important part of the process and care and attention must be paid to insure the patch is smooth and the surrounding surface is not scorched. Wave the knife in the flame and heat it until you can wipe off any and all residue of shellac from the knife. Gently heat the knife and slowly (in the same direction as the grain of the wood) draw the hot knife over the patch. Immediately wipe off the excess on the knife, re-heat and clean the knife thoroughly. Heat the knife and smooth the patch again. Just do a little at time don’t try and do too much at one time.
Some people prefer to apply an excess amount of shellac to the voids, and then use sharp chisels, scrapers or sandpaper to level the shellac. Use caution when leveling with these tools to prevent damage to surrounding surfaces. If you sand it is a good idea to use fine grit paper and lubricate the sandpaper with linseed oil to help produce a smooth finish. I have used other tools to level but I prefer to use the hot knife to apply the necessary and sufficient amount of shellac to the void, then use the clean hot knife to level and smooth the shellac to the final surface.
There are modern materials and tools that are available today that can make the work easier. Sticks are now offered in lacquer as well as shellac and plug in electric burning knives are on the market. The advantage of the electric model is that the heat is always there and it is never too hot avoiding some of the scorching problems one can have with lamp-heated knives. Modern lacquer sticks behave about the same as shellac sticks and available in the same colors including crystal clear.
With some repairs the color match of the sticks might be adequate for that purpose, but I seldom find a repair that needs just one color especially if wood or stain is missing. Most all old wood and finish are the color combination of wood, stain, finish and patina, therefore impossible to match with one color. Examine the area where the damage is and access what colors will be required. Some repairs will be in areas where there are two or more colors such as grain changing direction or the grain or pores of the wood. I start with the lightest color that is visible on the surround surfaces and do the main fill with this color. I then go over with another color stick that picks up the darker colors. I will sometimes at this point use regular shellac with some dry powdered pigments to add grain lines or subtle shades that I can’t achieve with the sticks. I then do a top fill with a light transparent stick to bring the fill up to optically flat with the surrounding surfaces.
The final stage is to heat the knife, clean it completely and use the hot knife to remove excess and make the fill perfectly flat. Sometimes the fill is to shiny for the surrounding surface and fine sandpaper or steel wool can be used to dull it down to the proper sheen. If there are grain lines or pore lines showing these can be added optically to the repair by using the edge of the hot knife to melt lines into the surface. Make the lines match the lines in the surrounding wood. After this technique is done a quick once over to smooth and ridges and give you the desired results.
If the color has not been damaged but the finish has voids, a transparent or clear stick can be used to just replace the missing finish. You are not replacing any color, just the missing finish. You want to match the optical flatness of the surrounding surfaces and any grain pattern that the original finish may telegraph through the finish. This may require you to put grain lines in the finish, which is done with the edge of a clean hot knife matching any intersecting grain or pore lines in the surrounding surface. Again take care when doing the final smoothing to avoid scorching the surround surfaces. Check the repair by sighting down the surface at a low angle to make sure the patch and finish are on the same plane.
Original shellac finishes are the most difficult to repair because the hot knife will also melt the surrounding shellac. Your knife needs to be hot enough to melt the stick but not too hot as to melt the surrounding surfaces. Old varnish or oil finishes are easier to repair, as they are harder than shellac. Modern finishes tend to be harder and are easier to repair providing that has cured properly and sufficiently. Fresh finishes that haven’t hardened enough can easily be damaged with the hot knife.
For darker colors you can always make your own burn in sticks with flake shellac and dry powdered pigments. The base color will be the natural color of the shellac, so select an appropriate grade of shellac for your purposes. They don’t necessarily need to be made in the shape of a stick. I have mixed up different colors in small tins and the hot knife can pick up the material and transfer it to the repair. If you use a small tin container you can carefully heat the container on the stove and mix in the pigments to achieve the desired color. I make mine by mixing flake shellac with rosin (75% shellac, 25% rosin) then using this as a base and add the dry powdered pigment as necessary. Make sure that the shellac/rosin/pigments are well mixed to insure uniform color throughout. If you don’t have access to rosin (available at music stores) you can use just straight shellac flakes. You can also mix in about 10% beeswax, which lowers the melting temperature but is a softer filler. This wax/shellac/rosin mixture is called Beaumontage stopping or simply ‘stopping’. It is faster than regular shellac or lacquer sticks but is softer and with the addition of the wax eliminates the ability to apply some finishes, as certain coatings won’t stick to the wax.
Another use of the hot knife is to steam out dents and dings in a surface prior to filling. The advantage is that only the finish will need to be replaced rather than filling up a deep hole. A drop or two of filtered or distilled water is placed in the dent and a wet cloth is placed over the dent and the clean hot knife is touched to the rag just over the damaged area. The hot knife will vaporize the water creating steam, which will quickly swell up the wood, in some cases back to the original level. This may require a couple of attempts to steam the dent out but can significantly reduce the amount of burn in stick required to make the surface perfectly level. Make sure that the area is perfectly dry before applying any hot shellac to the damaged area.
Repairing with hot stick shellac can take care of problems on large pieces of furniture that are difficult to move to the shop and on built in furniture. It is a good quick repair that is easily reversible for curatorial considerations. By using hot stick you can eliminate the need for a major restoration and maintain the integrity of the furniture, which is very important on antique pieces. Remember keep your knife clean and smooth.
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The shaving horse is a tool used by a number of trades including coopers, wheelwrights shingle makers and chair makers as well as a common tool used around the farmstead. It is a bench on which the worker sits with an adjustable jaw that holds the work fast as it is being shaped. While the shaving horses main use is to hold work while it is being shaped with a drawknife or spokeshave, it can also hold work being planed, drilled or any application where you need both hands free to do the work. The tool is also called a ‘schnitzel bank’, a mule, dumbhead or a bodger’s bench, depending on the place of origin.
The design varies from maker to maker but there are two basic varieties: one with a center lever with a block to hold the work and one with two side levers and a center bar that secures the work. The two designs have their advantages, the single lever can hold wider work but the double lever holds the work more securely but is limited to the width of the bench. The double lever is easier to build than the single lever model. The single lever is the most common type but both have ancient traditions.
The bench and ramp (working surface) are the same for both models. The bench needs to be long enough to have an adequate room to sit and work in front of the ramp. At times you want to sit a little closer to the ramp to do fine work and at other times you want to sit further back to work longer pieces. The elevation of the ramp should be enough to allow you to work without your hands hitting the bench while holding a drawknife.
The shape of the seat should be comfortable with rounded over edges, as you will be straddling the bench as you work. If you make the bench out of a wide board you can cut inward curves in the wide board to accommodate your legs.
The length of the benches legs should be long enough for comfortable seating so that your feet are on the floor and you can easily reach the foot peddle. You want to be at a comfortable height. Some old benches are slightly sloping with the seat legs higher and the ramp end a little lower. If this tool is going to be used in a permanent location then it is a good idea to cut saw kerfs in the ends of the legs and use wedges (and glue) to secure the legs in the sockets in the underside of the bench. This can be blind wedging (fox wedging) or the holes can be drilled through the bench seat and the wedges attached from the top. If you need to frequently transport, move or store the shaving horse then the legs can just be friction fit into the sockets. This allows the legs to be easily removed.
The jaws on the single lever model can be made of a large piece of wood and cut and shaped to the desired profile. It can also be built up from smaller pieces and pegged together. The lever connecting the jaws to the foot peddle should be constructed of a stout wood such as white oak or hickory. The jaws can be constructed of a hardwood, which will take a lot of wear but may dent the work being held. Jaws of a softer wood will not wear as well but will also not mare the stuff being worked on the shaving horse. The jaws of the double lever model need to be strong enough to take the pressure exerted by the foot. I prefer jaws on the double lever to pivot so the work of any shape can be fully engaged against the ramp. Some examples of the double lever jaws have a V-shaped notch on one sharp edge to hold square stock as it is being worked. The jaws on the single lever need to be rounded on the front edge to be able to engage any shaped piece that is worked. The rounded edge also reduces dents and damage to the work pieces.
On the single lever model there is an elongated mortice cut in the ramp and bench behind the upright support. There are a series of holes drilled horizontally in the ramp to allow the lever and jaws to be positioned either closer or further from the front edge of the ramp. The lever also has a series of holes to allow the jaws to be adjusted for thinner or thicker work. A pivot pin is run through the appropriate hole in the ramp and through the necessary hole in the lever for the thickness of the work. The pin should be stout enough to take the pressure exerted when using this tool. The foot pedal is a large stout dowel that passes through the bottom of the lever. It should be long enough to extend out each side a sufficient distance to allow you to easily engage the pedal to exert the pressure and hold the work fast.
On the double lever model there are also holes drilled horizontally in the ramp and in both levers. This allows for the same sort of adjustments as to position of the lever and thickness of material. The pivot pin goes through the hole in one of the levers, through the ramp hole and engages the lever on the other side. The foot pedal is secured between the two levers and can extend out on each side to give additional foot room.
There are several methods to make the jaws open by themselves when pressure is released on the foot pedal. A wooden spring can be attached to the end of the bench and a string is attached to the tip of the bow and the top of the jaws. The string is adjusted until it pulls the jaws open with no pressure on the foot pedal. As the pedal is pushed to engage the work, the bow bends a bit putting tension on the string and as the foot pressure is released the jaws will open to allow the work to be repositioned. Another method is to balance the design so that the jaws fall open automatically. This can be difficult as the jaws usually stick out ahead of the lever and by nature causes the jaws to close when there is no pressure on the pedal. This requires that you open the jaws before the work can be inserted rather than being open all the time. You can also put an extra weight on the foot pedal, which will cause the jaws to open with no foot pressure. By positioning the weight in front of the foot pedal to compensate for the center of gravity the jaws will open when pressure is released. The position of the counterweight depends on the design and center of gravity of the jaws, lever and foot peddle, and this can be done after this part of the bench is complete. This allows you to position the work without touching the jaws, which is an advantage when doing a lot of repetitive work on the shaving horse.
There is no greater pleasure than sitting astride a wooden bench you have constructed and working wood by hand. You can place the shaving horse outside and enjoy the weather and surroundings as you are shaping chair rungs, roughing out turning blanks, tapering shingles or just making pegs or dowels. If you have been doing any of these operations at the workbench in a vise, it will immediately become clear how much time you can save using this wonderful tool, besides you get to sit down and work.
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While I will usually opt for hot hide glue made from carefully mixing ground hide glue and water, letting it stand, then heating up the admixture in a cast iron double boiler on the stove until I get just the right consistency of glue, water and heat, adjusting each without it getting above 145°, not too thin, not too thick, streaming into a steady stream without beading up when the brush is raised 6 inches above the glue pot. Or I pick up the container of commercially available liquid hide glue and just squirt it out of the bottle.
The liquid, ready to use stuff in the bottle is quite serviceable, especially for such repairs as veneer damage, gluing old furniture back together, making a nice cracking medium, sizing wood for staining are among the uses of Liquid Hide Glue.
Hide glue was one of the first glues developed by people in antiquity. The stuff has always worked to fasten wood together with or without mechanical reinforcements. Liquid hide glue is an available version that allows all to use the finest glue that has ever been developed. This stuff is by far a much better choice for furniture construction and for repair work it is invaluable. It takes longer to dry than some modern glues but it has a much longer ‘open time’, in other words the surfaces and joints and bonding time can be worked, or repositioned or moved longer than other glues. On the down side, it is not waterproof but there are things you can do to the glue to make it more resistant to water. It can take 24 hours for the glue to dry, but under some conditions it will be dry and ready to unclamp in as little as 8 hours. I always plan my glue-ups later in the day to make sure the stuff in under clamp overnight or 8 or 10 or 12 hours. The lower the temperature and higher the humidity the longer it will take for the hide glue to set up.
This is a water based product, so the moisture that is in the glue will absorb into the wood, therefore after the glue has set for 15 minutes or so, the clamps should be re-tightened to snug up the joint and make it stronger.
At times I will dampen the wood in the joint or the veneer to help the glue penetrate the wood and help the glue adhere to the surfaces. Also I prepare the surfaces prior to gluing by roughing it up to enhance the ability for the glue to grip and hold the wood. Traditionally a toothing scraper or plane was used to tooth or key the wood and veneer to prepare it for gluing. This intentional roughing of the substrate and joint surfaces is based on ancient traditions. Our forebears had thought this out and determined that the intentional roughing would improve the glues holding abilities.
When repairing buckled veneer I will put some liquid hide glue in a container and add a drop of glycerin and mix it in thoroughly. I then spread the glue on both sides of the veneer damage and allow it to soak into the substrate and both sides of the veneer. I then use a clear plastic block to clamp down the buckled veneer. I then remove the block and wipe it and the surface of excess glue and dry with a rag. I then re-clamp the block on the damage and allow to dry overnight. The glycerin will help the buckled veneer from splitting and cracking, it makes it softer and easier to work. If I have to use a hypodermic syringe to inject the liquid hide glue into a joint or beneath veneer I will warm the glue and needle in hot water to reduce the viscosity making it easier to go through a very small needle. The glycerin also makes the glue slightly flexible which can be of help when re-gluing canvas onto the back of a tambour or roll-top desk.
Liquid hide glue has a shelf life and an expiration date. I have to admit that I have used old out dated liquid hide glue from time to time and it seems to work but I am sure it is best if it hasn’t got too old. Buy smaller containers if you don’t use a lot so it doesn’t go bad. If you are using more, and you should, you can purchase it in larger containers. I have a larger bottle that I transfer into a smaller one that is easier to handle than the larger size. Because it is water based I imagine that it should be protected from freezing, I have never had any freeze and do not know if it degrades the glue after a freezing cycle. If it is cold in the shop I will place the container of glue in a bowl of warm water to help keep the stuff flowing. Nothing like waiting for the thick cold hide glue to slowly work its way down the inside of the bottle, as it takes its time to get to the nozzle and requires excess pressure on the plastic bottle to force a little cold dollop of glue out the tip, can be frustrating. The same warm water can be used to brush on the joints at the glue surfaces to promote a better glue bond.
Liquid hide glue is also an excellent medium to use for making cracked and crackled finishes, See Cracked and Crazed Finishes for details on its use.
Hide glue and liquid hide glue are both moderately good gap fillers. Although the strength of a joint should be in the wood with a tight and proper fitting joint, the glue should not be used as a replacement for wood. If you have slight gaps and do need to fill, add wood flour, that is very fine wood saw dust of the matching wood to the hide glue, mix thoroughly and brush on to all the joint glue surfaces.
There is a material that can be added to hot hide glue or liquid hide glue to make it more water resistant. By adding a small amount of isinglass (float bladders from sturgeon fish) is mixed with water then added to the hide glue before it is applied. This material is available at wine or beer making supply companies as it is used to clarify wine and beer. You need to experiment as to how much of this stuff to add, try around 10% and see how it goes.
I use a small stiff bristled brush for applying glue. You can also use a small round paint brush with stiffer bristles or hairs and if they are too soft, you can make a wire bridle to wrap around the bristles half way up from the ferrule, then down to bind around the ferrule. This makes the brush last longer and help hold the hairs together when applying the hide glue to the inside of a narrow mortice or chair leg socket.
There are a couple of schools of thought about how to clean off excess hide glue that is forced from the joints as the clamps are tightened. While some prefer to wait and let the glue become a little gummy before they remove the stuff with a putty knife or scraper. Some prefer to allow it to dry for several hours then use a scraper to ‘pop’ off the dryer glue residue. Others prefer to use a putty knife and remove the glue immediately, then using a wet rag to wipe off all traces of the glue residue. I usually remove the glue immediately and wipe with a wet cloth. There should always be residue to remove; always use enough glue to completely cover all surfaces and fill all areas, glue is cheap.
Liquid hide glue will contain chemicals that keep it in liquid form that are dangerous and you should avoid ingesting the glue, even though it is pure protein. These chemicals such as urea also kill bugs or at least dissuade them from eating the glue, which can be a problem.
Liquid hide glue is by far one of the finest glues on the market today. Its application for furniture repair and restoration, musical instrument making and repair, for veneer repair work or for just gluing a loose chair together, this stuff can’t be beat. It works for furniture construction and gluing small objects made of wood together. You can even hammer veneer with liquid hide glue.
I have used and can hardily recommend Old Brown Glue made by W. Patrick Edwards. It is thicker than other commercial liquid hide glues. There is a link to his web site on the Links Page.
The problem of cross grain has been around for centuries. Cross grain that I am talking about is where one or more pieces of wood are joined to another piece where the grain is running perpendicular to each other. Wood shrinks and expands across the width of the grain but there is very little movement along the grain of the wood. So when wood is mounted cross grain there can be problems with one piece of wood wanting to move and the other piece not moving at all. The end result can be splitting and cracking of the field boards, an end cap that is either proud or shy of the boards or as a substrate for veneering, buckled veneer.
The reason cross grain is used is to hide the end grain of table tops such as with a breadboard or mitered end cap. Breadboard ends are also used to stabilize boards used in substrates for veneering. Cross grain also occurs when moldings are added to cabinets at 90° to the grain of the panels. Cock beading around drawer fronts or doors can also present a problem.
For breadboard or mitered end caps, the best way to reduce problems with cross grain is to use quartersawn wood for the boards on top or panel. This is the most stable cut of wood and the movement; either expansion or contraction is greatly reduced using wood that has quartersawn grain. Even with quartersawn wood there will still be some movement, there is just no stopping wood from moving that is its nature. The problem occurs when the end cap is attached to the boards of the panel or top. The traditional method of attaching end caps to breadboards is to use a tongue and groove joint. A tongue or tenon is formed on the ends of the boards and a groove is formed on the end cap. This secures the boards and helps prevent the boards from warping and covers the end grain of the boards. Some breadboards have a loose tenon or spline that is placed in a groove in the end cap and on the boards. This technique may help reduce problems such as cracking and splitting of the boards but if it is fastened too securely it can cause the same problems as a regular breadboard end.
If the originating craftsman took into consideration these movements and problems they can be ameliorated by doing certain things during the construction process. Old pieces of furniture were invariably glued together with hot hide glue. Hide glue is thermoplastic and if the stresses of movement are slow enough the glue will creep allowing the pieces to adjust without splitting or other damage. If the movement is too quick such as rapid changes in temperature and humidity the glue will not move resulting in the subsequent damage. A technique for making hide glue more amenable is to add a drop or two of glycerin to the glue before it is applied; this keeps the glue slightly flexible.
Many breadboard ends are nailed or pegged together at the tongue and groove joint and this is where the problems begin. If the fasteners keep the boards from free movement the result will be splits and cracks. In order to prevent this problem the holes are drilled for the pegs or a bradawl is used to make the holes for the nails. This is done while the boards and end cap are assembled but before the glue is applied. The joint is taken apart and the holes on the tongue on each side of the center are elongated. The center peg or nail hole can be left alone as this will allow the movement to occur on both sides of the center of the panel or top. By elongating the holes (on the cross grain tongue) the pegs or nails will hold the end cap secure but allow the boards to move. Also just applying glue to the center of the breadboard joint around the peg or nail without an elongated hole will help hold the end cap and still allow for movement.
Remember with breadboard ends there will be movement and during certain times of the year the end cap will protrude out from the boards and at other times of the year the boards will project out from the end cap. This is the nature of this joint, you just have to accept that there will be movement.
Cock beading around drawer fronts can also present a problem as the bead on the ends of the drawers are applied cross grain. All were glued onto the sides of the drawer front and some were nailed using fine cut headless brads. I have repaired many pieces of furniture with problems at the cock bead. I live in the dry West, which is an ideal location for furniture because it is so dry. Most antiques were produced in other parts of the country or world and when they come out here, they dry out and shrink. As the drawer front shrinks across grain the cock bead molding on the ends do not move which results in the mitered corners coming loose from the force of the little bead not moving. This is fairly easy to correct in the case where it has shrunk, as the cock bead can be re-mitered at the corners to produce a perfect fit. However if the piece then goes to an area of higher humidity, the front can expand leaving gaps at the miter. The vast majority of cases are that the drawer front shrinks and the repairs can be done at the corners. Cock beading around framed rail and style doors present less of a problem because it only has cross grain at the ends of the narrow styles on the top and bottom of the door. If it is a slab or slab and veneered door the problems are the same as with a drawer fronts where the molding is glued and nailed to the cross grain field. I recommend gluing the cross grain cock bead just in the center and use small brads to secure the molding on both sides of the glue. The miter can also be glued.
On old pieces and even on new work when molding is applied to furniture it can in some cases be a cross grain situation. One method that was used to help prevent problems was just to use fine cut nails to attach the molding to the cabinet and not use glue at all. The soft wrought iron nails will bend in some cases and any movement may adjust. Problems can occur at the miters, which can be easily repaired, and many old pieces will have the molding projecting out the backside of the cabinet as the boards shrink across grain and the molding retains much of its original length. As with cock bead the best method is to apply glue just in the center and brad the molding on both sides of the glue. The miters can also be glued to help hold the corners together. You may just want to glue the miters and the front of the molding to the casework, then allow the end to float and move freely.
Some old furniture will have pieces in dados or dovetail dados across the grain, such as drawer runners or dust dividers that can present a cross grain problem if they are fastened too securely. The problems can be reduced by attaching the cross grain pieces in the center and allowing the ends to float freely in the dado or dovetail dado. Some pieces are attached just at the front edge that shows and the back is allowed to move freely.
Whether you are making new furniture or dealing with old pieces, cross grain can be a problem but with proper planning and skillful execution the work can be done to greatly reduce problems that will occur with subsequent movement of the wood. Keep in mind that wood always moves unless it has been turned into a fossil, the movement of petrified wood is microscopic but even stone expands as it is warmed and contracts when it cools. Use quartersawn wood when possible, make sure the wood is dry, elongate any peg or nail holes, apply glue only to the center of the joints and offer supplication.
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