Meyer Bar Coating
There are many published ways to coat a surface with a Meyer bar but most describe coating just a small area on the surface. Here is describe two methods for coating entire surfaces beneficial for holographic emulsion coating.
This method does the best job that I have found and is depicted in the diagram below.
- Take a glass size and determine what size plates you wish to coat.
- Clean and sub the entire glass sheet so that it is ready to coat. In the drawing below we are doing 4 - 4inch by 5inch plates.
- Make the full size glass 2 inches larger in width(1 inch on each side) and 4 inches larger in length (3 inches at top and 1 inch at bottom).
- Score the glass with a glass cutter as shown but do not break any of the scores. This needs to be done on a very flat, clean and rigid surface.
- Now clean the scored side from all glass chips. A wet paper towel will do nicely. TURN THE PLATE OVER. It is recommended to perform the following procedure in 80F to 90F ambient temperature or heat the glass and rod with a warm air blower (hair dryer) until warm to the touch. Also, the surface should be level in both directions.
- Place the Meyer bar (ROD) at the top of the pre-scored plate.
- Pour a puddle of heated emulsion across the top as shown and immediately draw the Meyer bar down the length of the plate with an even pressure and speed. You will notice the puddle stay in front of the bar and continue util you are off the bottom of the plate.
- Wait until the emulsion is dry (this can be tested at any four of the discard ends).
- Take a razor blade and score (cut) the emulsion down each of the scores (the scores are still on the bottom and you are cutting the emulsion on the top).
- TURN THE PLATE OVER and break the scores as you would with any scored glass keeping care to not let the emulsion surface touch anything. This becomes easy with practice by keeping the end your are breaking in you hand and keeping the fixed end remain on the glass cutter knob (see Glass Cutting). Break all the longest lenghts first (top, bottom, two sides then the plates). This gives very even and uniform coatings for each glass.
In the next technique, which can be modified for more plates, we will coat 4 - 4inch by 5inch plates.
- Take the 4 cleaned glass plates and place them in a rectanglur fashion such that the rectangle is 8 inches across and 10inches down on a level surface.
- Now take two additional cleaned 4x5 plates (puddle plates) and lay then such that they are 10 inches across at the top of the rectangle. They will overhang the rectangle 1 inch on each side.
- Now use thin clear gift tape (Scotch brand works well) to tape aound the rectangle of plates (not the top two, they will be used to pour the puddle onto) and where each plate meet another plate. Each of the four plates will have tape around all four of their sides. Make sure the tape is flattened nicely to the plate with your finger. Again use the same temperature restraints as described above (ambient or blow heater).
- Place the Meyer bar at the top of the puddle plates.
- Pour the heated emulsion across the center of the top two puddle plates and immediately draw the Meyer bar down the plates and off the end of the plate as described above.
- Let the plates set for only one hour, then remove the tape. Allow the plates to continue to dry lying horizontally.
This too yields very consistant results. This method uses the tape for some of the emulsion thickness (the Meyer bar is off the glass by the thickness of tape) so the Meyer bar should be finer the in the above proceedure.
- Plate, emulsion and Meyer bar temperatures affect coating thickness to a small extent but if the temperature is too low on any of these, gelation may occure and quality compromised.
- Meyer bars come in different gauges which is the thickness of the wire that is wound. Usually a #40 is .04", a #25 is a .025 inch etc.. I have found a #25 to #40 works very well in either case with the #40 producing thicker emulsion.
- Meyer bars should be soaked immediately in warm water to keep the gelatin from hardening on the bar, then washed with hot water and dried.
Meyer Bar Selection -