22 



HARDWOOD RECORD 



October 10, 1922 



Rosin and Lampblack Vs. Red Lead and Oil 



Their Relative Value as Coatings to Prevent End Checking of 



Stock During Kiln Drying 



By James D. Studley 



Assistant Wood Technologist Forest Products Laboratory 

 United States Forest Service Madison, Wisconsin 



Rosin and Lampblack 



There is probably no end coating more universally applied to 

 minimize end checking in the kiln drying of refractory hardwoods 

 than a heavy mixture of red lead and oil. There are few mixtures, 

 on the other hand, less used commercially than rosin and lampblack. 

 Differences of opinion concerning the relative effectiveness of the 

 two coatings led to their comparison on a commercial scale by 

 the Forest Products Laboratory, Madison, Wisconsin. The study 

 was made at the plant of the Mandt Wagon Company, Stoughton, 

 Wisconsin. 



Arkansas swamp oak bolster stock of heavy sizes was used in 

 the study. Of the 905 pieces end-coated, 506 were of the 

 "heavy regular" {VilTV^") class, 175 of the "standard regular" 

 (3%"x7%") class, and 224 were of the "medium regular" (3i4"x7") 

 class. The stock had dried in the yard to an average moisture 

 content of from 50 to 72 per cent prior to its use in the study; 

 and the end checking resulting from yard seasoning had affected 

 practically every piece, so that only the relative influence of the 

 two end coatings could be determined. 



No Variables in Stock or I.oading 

 Every effort was made to secure an absolute uniformity of stock 

 between the two end-coating groups. As the loads of stock came 

 to the kiln they were divided into halves, one being immediately 

 given the rosin and lampblack treatment, the other the red lead and 

 oil treatment. To eliminate any variation in drying conditions 

 between the two end coating groups, pieces from each end coating 

 class were placed next each other in all parts of the kiln. The 

 average condition of the stock, from the standpoint of end check- 

 ing in each of the two end-coating classes and the average drying 

 conditions imposed on each class, was thus practically uniform. 



End-Coating Treat- _^___ 



ments 

 The red lead and 

 oil mixture was pre- 

 pared by grinding 

 70 pounds of red 

 lead into one gallon 

 of oil, composed of 

 2 quarts of raw lin- 

 seed oil, 1 quart of 

 naphtha, and 1 quart 

 of varnish. The 

 rosin and lampblack 

 mixture was made 

 up by heating to- 

 gether 30 parts by 

 weight of rosin to 

 one of lampblack. 

 Both end coatings 

 were applied to the 

 bolsters with 

 brushes just prior to 

 the loading of the 

 stock into the kiln. 

 Some attention was 

 needed to see that 

 the rosin and lamp- 



RED LEAD—OIL 



RED LEAD — OIL ^ 

 ROSIN— LAMPBLACKl 



RED LEAD — OIL 



ROSIh— LAMPBLACK 



I 



black mixture was at the proper temperature for application and 

 that it gave the proper thickness of coating, but otherwise no 

 particular discrimination in application was made. 



Drying Conditions 



All the stock was dried in the same kiln charge and in a kiln 

 where drying could be kept practically uniform throughout. The 

 kiln temperature ranged from 100° to 135° Fahrenheit and the 

 relative humidity from 100 to 40 per cent. Steaming treatments 

 at temperatures as high as 175° and for as long as two hours were 

 imposed. It is thus seen that the end coatings were subjected 

 to quite severe drying conditions. The stock was dried to an 

 average moisture content of 10 per cent and then taken to the 

 factory. 



Determination of Coating Effectiveness 



Within each size class of bolster stock a comparison was made 

 of the honeycomb resulting in each of the end coating groups. To 

 determine the amount of honeycomb present in a bolster, a section 

 averaging an inch in length was cut from each end, and the four 

 sides were surfaced. During this procedure and until such time 

 afterwards as the honeycomb determinations were made, all stock 

 of an end-coating group was kept together as a unit. The honey- 

 comb determinations were made by measuring the maximum width 

 of the widest honeycomb, both ends of the bolsters being con- 

 sidered, and classifying the bolster according to this width. A 

 bolster having a honeycomb 2.86 mm. (1 mm. = 0.0394 inch) in 

 width, for instance, and another 2.07 mm. in width would be thrown 

 to the 2.35-3.50 mm. class. The four arbitrarily chosen width 

 classes are as follows: (1) honeycomb 0.10-1.10 mm. in width; (2) 

 honeycomb 1.10-2.35 mm. in width; (3) honeycomb 2.35-3.50 mm. 



in width; (4) honey- 

 comb over 3.50 mm. 

 in width. In addi- 

 tion to these there 

 were two other 

 classes into which 

 some stock fell — the 

 "perfect" class 

 and the "reject" 

 class. The perfect 

 class embraced 

 stock with no defect 

 in either end, the 

 reject class that 

 with so much honey- 

 comb as to make it 

 unfit for use as a 

 bolster. 



In each size class 

 and in each of its 

 end-coating groups 

 the percentage of 

 bolsters falling to 

 each honeycomb 

 width class was 

 then calculated. A 

 direct comparison 





..■„„„.... I „- KV^VVV^V^VVx^^vvv\xN-'.lAVkVV^^NVVvvv\AVW^^-^---^^tl 



IN HEAVY RCOULAR CLASS 



STAtlDARO REGULAR 



I— -^1 \ 





IM MEDIUM REGULAR CLASS 



Chart showing the loss from honeycombing in three classes ot bolsters, end-coated with red lead and 



oil and with rosin and lampblack 



