24 



HARDWOOD RECORD 



October 10. 1922 



A truck load of average bolster stock (rosin end dip) after planing and equalizing 



by size classes of 

 these percentages 

 is shown on the 

 accompanying bar 

 graph. It can be 

 quickly seen th.at in 

 "heavy regular" 

 size class the rosin 

 and lampblack coat- 

 ing was by far the 

 superior. A smaller 

 percentage of re- 

 jects and a larger 

 percentage of per- 

 fect s t o ck was 

 found. In the 

 "medium regular" 

 class it may again 

 be seen that the 

 rosin and lampblack 

 mixture was with- 

 out question the bet- 

 ter coating. Though 

 neither end-coating 

 contained any re- 

 jects, all the stock 

 in the rosin and 

 lampblack group 

 fell within the 

 "perfect" or "honeycomb 0.10-1.10 mm." class, while in the red 

 lead and oil group nearly a quarter of the total number fell below 

 these classes. In the "standard regular" size class the superiority 

 of the rosin and lampblack coating is not quite so apparent, as it 

 has more rejects than the red lead and oily group. More of the 

 stock coated with the rosin and lampblack, however, is included 

 in the perfect and near perfect groups than that coated with the 

 red lead and oil mixture. 



The effectiveness of the two end coatings is illustrated by the 

 two photographs accompanying this article. Both show stock of 

 the "heavy regular" size class, and each is representative of the 

 average condition of the stock in its end-coating group. The 

 contrast is decidedly in favor of the rosin and lampblack coating. 



Kostn Prejudice 

 Considered 



In view of the 



demonstrated superi- 

 ority of the rosin 

 and lampblack mix- 

 ture, the reasons for 

 the prejudice 

 against its use are 

 of interest. 



The complaint is 

 made that since the 

 rosin mixture must 

 he hot it is incon- 

 venient to apply. 

 This objection is 

 hardly justified, 

 since the rosin mix- 

 ture may be painted 

 on with no par- 

 ticular difficulty, 

 just as was done in 

 the study. If a pot 

 similar to a solder 

 pot were used and 

 a constant amount 

 of heat applied, the 



mixture could be 

 kept at such uni- 

 form temperature 

 and viscosity that it 

 would be just as 

 easily applied as a 

 cold mixture. Fur- 

 thermore, the rosin 

 mixture hardens as 

 soon as applied, so 

 that a coating of 

 the desired thick- 

 ness may be quickly 

 built up; whereas 

 with the red lead 

 and oil, a thick 

 coating tlows off be- 

 fore it can dry. 



It is contended 

 that the use of the 

 rosin and lampblack 

 mixture slows down 

 factory operation 

 and that increased 

 upkeep and manu- 

 facturing charges 

 result from its use. 

 This is a legitimate 

 claim if the mixture 



A truck load of averagre bolster stock (red lead and dip) after planing and equalizing 



is recommended indiscriminately, but not when it is advocated for 

 use on turning squares or for any part where the ends are trimmed 

 as the first factory operation. 



The cost of the mixture is sometimes advanced as an argument 

 against its use. On the basis of present quotations and a con- 

 sideration of the relative surface spreads, however, the rosin and 

 lampblack is the more economical. Use rosin and lampblack in 

 preference to red lead and oil as an end coating for the minimiz- 

 ing of honeycomb losses in refractory hardwoods. This is the con- 

 clusion reached in this s udy. It must not be inferred, however, 

 that a rosin and lampblack mixture should be used in preference 

 to end coatings other than red lead and oil. The relative effective- 

 ness of other end coatings is now being determined at the Forest 



Products Laboratory 

 Rosin and lamp- 

 black is recom- 

 mended in prefer- 

 ence to lead and oil 

 because (1) the 

 rosin and lampblack 

 is decidedly more 

 effective than the 

 red lead and oil 

 mixture; (2) it is 

 practically as easily 

 applied; (3) the de- 

 sired thickness of 

 coating is more 

 readily obtained on 

 the ends of the 

 pieces; and (4) last, 

 but not least, the 

 fluid-like property of 

 the rosin allows it 

 to flow during the 

 drying of the stock 

 and thus keeps the 

 coating intact in 

 spite of drying de- 

 fects. 



